C1: deploy adelaide-baby-shower-app to ringtail k3s (#349)

## Summary

Brings up the Adelaide / Heidi / Addie baby shower app on ringtail k3s with the public/private split that the app's hosting contract calls for: `shower.eblu.me` (public, via Fly proxy) and `shower.ops.eblu.me` (tailnet). App is consumed as a wheel from the Forgejo PyPI index — source lives at [`adelaide-baby-shower-app`](https://forge.eblu.me/eblume/adelaide-baby-shower-app).

### What's included

- **ArgoCD app + manifests** under `argocd/manifests/shower/` (deployment, service, ProxyGroup ingress, ConfigMap for `DJANGO_DEBUG`/`DJANGO_ADMIN_URL`, ExternalSecret for `DJANGO_SECRET_KEY` from 1Password item `Shower (blumeops)`, NFS PV on sifaka, RWX media PVC, RWO local-path data PVC for SQLite). Recreate rollout because SQLite is single-writer.
- **Public surface** (`fly/`): new `shower.eblu.me` server block proxying to `shower.ops.eblu.me`. `/admin/` returns 403 at the edge except `/admin/login/` and `/admin/logout/`, which are rate-limited via a new `shower_auth` zone. `X-Clacks-Overhead` on. GNU Terry Pratchett.
- **fail2ban** filter (`shower-admin-login.conf`) matching 401/403/429 on `/admin/login/` and jail (`shower.conf`) with `maxretry=5/findtime=600/bantime=3600`. The `nginx-deny` action was generalized to take a per-jail `nginx_deny_file` so the shower has its own deny list (forge keeps using the legacy default).
- **Caddy** route on indri (`shower.ops.eblu.me` → `https://shower.tail8d86e.ts.net`).
- **Pulumi** Gandi CNAME `shower.eblu.me → blumeops-proxy.fly.dev.`.
- **Grafana** APM dashboard `configmap-shower-apm.yaml` (request rate, error rate, failed admin login count, latency percentiles, bandwidth, access logs) mirroring `docs-apm.json` with a `host="shower.eblu.me"` filter.
- **Container** `containers/shower/default.nix` — `dockerTools.buildLayeredImage` with a nixpkgs Python and a startup wrapper that creates `/app/data/.venv`, pip-installs `adelaide-baby-shower-app==1.0.0` from the forge PyPI index on first boot, runs migrations + collectstatic, and execs gunicorn. A `local_settings.py` shim pins `DATABASES.NAME`/`MEDIA_ROOT`/`STATIC_ROOT` to absolute paths so they don't end up in site-packages.
- **Docs** runbook at `docs/how-to/operations/shower-app.md` linked from the apps registry, plus changelog fragments.

### Defense layers on the public surface

1. fly nginx geo+fail2ban `$shower_banned` (per-service deny list)
2. fly nginx `limit_req zone=shower_auth` (3 r/s per Fly-Client-IP)
3. django-axes (5 fails / 1h, keyed on username+ip_address)
4. edge `/admin/` block (returns 403 for anything that isn't login/logout)

## Prerequisites for the user to do (NOT in this PR)

Halted on these per request — they touch shared/manual systems:

- [x] **NFS share** on sifaka: `/volume1/shower`, NFS rule for ringtail RW, `chown 1000:1000`
- [ ] **1Password item** `Shower (blumeops)` in the blumeops vault with a freshly minted `secret-key` field (`openssl rand -base64 48`) — do NOT reuse anything that has lived in git
- [ ] **Container build**: `mise run container-build-and-release shower`, then update `images[].newTag` in `argocd/manifests/shower/kustomization.yaml` to the resulting `v1.0.0-<sha>-nix`
- [x] **DNS**: `mise run dns-up` after merge
- [x] **Fly cert**: `fly certs add shower.eblu.me -a blumeops-proxy`
- [ ] **Caddy push**: `mise run provision-indri -- --tags caddy`
- [ ] **Fly redeploy** to pick up the new nginx block + fail2ban jail: `mise run fly-deploy`
- [ ] **ArgoCD sync**: `argocd app set shower --revision shower-app-deploy && argocd app sync shower` to test from this branch before merging

## Test plan

- [ ] Container builds successfully on nix-container-builder runner
- [ ] Pod starts, migrations run, gunicorn answers on :8000
- [ ] `kubectl --context=k3s-ringtail -n shower logs deploy/shower` clean
- [ ] `curl -sf https://shower.ops.eblu.me/` returns the splash page (tailnet)
- [ ] `curl -I -H "Host: shower.eblu.me" https://blumeops-proxy.fly.dev/` returns 200 (pre-DNS verification)
- [ ] `curl -I -H "Host: shower.eblu.me" https://blumeops-proxy.fly.dev/admin/users/` returns 403 (edge block)
- [ ] `curl -I -H "Host: shower.eblu.me" https://blumeops-proxy.fly.dev/admin/login/` returns a Django login response
- [ ] After DNS is up: `curl -I https://shower.eblu.me/` returns 200 with `X-Clacks-Overhead`
- [ ] Grafana dashboard "Shower APM" appears and starts showing traffic
- [ ] `mise run services-check` passes

Reviewed-on: #349

argocd/manifests/grafana-config/dashboards/configmap-shower-apm.yaml

@@ -0,0 +1,229 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: grafana-dashboard-shower-apm
+  namespace: monitoring
+  labels:
+    grafana_dashboard: "1"
+data:
+  shower-apm.json: |
+    {
+      "annotations": { "list": [] },
+      "editable": true,
+      "fiscalYearStartMonth": 0,
+      "graphTooltip": 1,
+      "id": null,
+      "links": [],
+      "panels": [
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "fieldConfig": {
+            "defaults": {
+              "color": { "mode": "palette-classic" },
+              "custom": {
+                "axisLabel": "req/s",
+                "drawStyle": "line",
+                "fillOpacity": 20,
+                "lineInterpolation": "linear",
+                "lineWidth": 1,
+                "showPoints": "never",
+                "spanNulls": false,
+                "stacking": { "group": "A", "mode": "normal" }
+              },
+              "mappings": [],
+              "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }] },
+              "unit": "reqps"
+            },
+            "overrides": []
+          },
+          "gridPos": { "h": 8, "w": 16, "x": 0, "y": 0 },
+          "id": 1,
+          "options": {
+            "legend": { "calcs": ["mean", "max"], "displayMode": "table", "placement": "right", "showLegend": true },
+            "tooltip": { "mode": "multi", "sort": "desc" }
+          },
+          "targets": [
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "sum by (status) (rate(flyio_nginx_http_requests_total{host=\"shower.eblu.me\"}[5m]))", "legendFormat": "{{status}}", "refId": "A" }
+          ],
+          "title": "Request Rate by Status",
+          "type": "timeseries"
+        },
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "fieldConfig": {
+            "defaults": {
+              "color": { "mode": "thresholds" },
+              "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }, { "color": "yellow", "value": 0.01 }, { "color": "red", "value": 0.05 }] },
+              "unit": "percentunit"
+            },
+            "overrides": []
+          },
+          "gridPos": { "h": 4, "w": 8, "x": 16, "y": 0 },
+          "id": 2,
+          "options": {
+            "colorMode": "background",
+            "graphMode": "area",
+            "justifyMode": "center",
+            "orientation": "auto",
+            "reduceOptions": { "calcs": ["lastNotNull"], "fields": "", "values": false },
+            "textMode": "auto"
+          },
+          "targets": [
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "sum(rate(flyio_nginx_http_requests_total{host=\"shower.eblu.me\",status=~\"5..\"}[5m])) / sum(rate(flyio_nginx_http_requests_total{host=\"shower.eblu.me\"}[5m]))", "refId": "A" }
+          ],
+          "title": "Error Rate (5xx)",
+          "type": "stat"
+        },
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "fieldConfig": {
+            "defaults": {
+              "color": { "mode": "thresholds" },
+              "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }, { "color": "yellow", "value": 1 }, { "color": "red", "value": 5 }] },
+              "unit": "short"
+            },
+            "overrides": []
+          },
+          "gridPos": { "h": 4, "w": 4, "x": 16, "y": 4 },
+          "id": 3,
+          "options": {
+            "colorMode": "background",
+            "graphMode": "area",
+            "justifyMode": "center",
+            "orientation": "auto",
+            "reduceOptions": { "calcs": ["lastNotNull"], "fields": "", "values": false },
+            "textMode": "auto"
+          },
+          "targets": [
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "sum(increase(flyio_nginx_http_requests_total{host=\"shower.eblu.me\",request_uri=~\"/admin/login.*\",status=~\"4..\"}[$__range]))", "refId": "A" }
+          ],
+          "title": "Failed admin logins (range)",
+          "type": "stat"
+        },
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "fieldConfig": {
+            "defaults": {
+              "color": { "mode": "thresholds" },
+              "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }] },
+              "unit": "reqps"
+            },
+            "overrides": []
+          },
+          "gridPos": { "h": 4, "w": 4, "x": 20, "y": 4 },
+          "id": 4,
+          "options": {
+            "colorMode": "value",
+            "graphMode": "area",
+            "justifyMode": "center",
+            "orientation": "auto",
+            "reduceOptions": { "calcs": ["lastNotNull"], "fields": "", "values": false },
+            "textMode": "auto"
+          },
+          "targets": [
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "sum(rate(flyio_nginx_http_requests_total{host=\"shower.eblu.me\"}[5m]))", "refId": "A" }
+          ],
+          "title": "Current RPS",
+          "type": "stat"
+        },
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "fieldConfig": {
+            "defaults": {
+              "color": { "mode": "palette-classic" },
+              "custom": {
+                "axisLabel": "seconds",
+                "drawStyle": "line",
+                "fillOpacity": 10,
+                "lineInterpolation": "linear",
+                "lineWidth": 1,
+                "showPoints": "never",
+                "spanNulls": false,
+                "stacking": { "group": "A", "mode": "none" }
+              },
+              "mappings": [],
+              "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }] },
+              "unit": "s"
+            },
+            "overrides": []
+          },
+          "gridPos": { "h": 8, "w": 12, "x": 0, "y": 8 },
+          "id": 5,
+          "options": {
+            "legend": { "calcs": ["mean", "max"], "displayMode": "table", "placement": "right", "showLegend": true },
+            "tooltip": { "mode": "multi", "sort": "desc" }
+          },
+          "targets": [
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "histogram_quantile(0.50, sum by (le) (rate(flyio_nginx_http_request_duration_seconds_bucket{host=\"shower.eblu.me\"}[5m])))", "legendFormat": "p50", "refId": "A" },
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "histogram_quantile(0.90, sum by (le) (rate(flyio_nginx_http_request_duration_seconds_bucket{host=\"shower.eblu.me\"}[5m])))", "legendFormat": "p90", "refId": "B" },
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "histogram_quantile(0.99, sum by (le) (rate(flyio_nginx_http_request_duration_seconds_bucket{host=\"shower.eblu.me\"}[5m])))", "legendFormat": "p99", "refId": "C" }
+          ],
+          "title": "Latency Percentiles",
+          "type": "timeseries"
+        },
+        {
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "fieldConfig": {
+            "defaults": {
+              "color": { "mode": "palette-classic" },
+              "custom": {
+                "axisLabel": "",
+                "drawStyle": "line",
+                "fillOpacity": 20,
+                "lineInterpolation": "linear",
+                "lineWidth": 1,
+                "showPoints": "never",
+                "spanNulls": false,
+                "stacking": { "group": "A", "mode": "none" }
+              },
+              "mappings": [],
+              "thresholds": { "mode": "absolute", "steps": [{ "color": "green", "value": null }] },
+              "unit": "Bps"
+            },
+            "overrides": []
+          },
+          "gridPos": { "h": 8, "w": 12, "x": 12, "y": 8 },
+          "id": 6,
+          "options": {
+            "legend": { "calcs": ["mean", "max"], "displayMode": "table", "placement": "right", "showLegend": true },
+            "tooltip": { "mode": "single", "sort": "none" }
+          },
+          "targets": [
+            { "datasource": { "type": "prometheus", "uid": "prometheus" }, "expr": "sum(rate(flyio_nginx_http_response_bytes_total{host=\"shower.eblu.me\"}[5m]))", "legendFormat": "Bandwidth", "refId": "A" }
+          ],
+          "title": "Bandwidth",
+          "type": "timeseries"
+        },
+        {
+          "datasource": { "type": "loki", "uid": "loki" },
+          "gridPos": { "h": 8, "w": 24, "x": 0, "y": 16 },
+          "id": 7,
+          "options": {
+            "dedupStrategy": "none",
+            "enableLogDetails": true,
+            "prettifyLogMessage": false,
+            "showCommonLabels": false,
+            "showLabels": false,
+            "showTime": true,
+            "sortOrder": "Descending",
+            "wrapLogMessage": false
+          },
+          "targets": [
+            { "datasource": { "type": "loki", "uid": "loki" }, "expr": "{instance=\"flyio-proxy\", job=\"flyio-nginx\"} |= \"shower.eblu.me\" | json | line_format \"{{.client_ip}} {{.request_method}} {{.request_uri}} {{.status}} {{.request_time}}s\"", "refId": "A" }
+          ],
+          "title": "Recent Access Logs",
+          "type": "logs"
+        }
+      ],
+      "refresh": "30s",
+      "schemaVersion": 38,
+      "tags": ["shower", "flyio", "apm"],
+      "templating": { "list": [] },
+      "time": { "from": "now-6h", "to": "now" },
+      "timepicker": {},
+      "timezone": "",
+      "title": "Shower APM",
+      "uid": "shower-apm",
+      "version": 1,
+      "weekStart": ""
+    }