Wave 1 indri→ringtail migration: paperless, teslamate, mealie (#363)

Migrate paperless, teslamate, and mealie off the OOM-saturated minikube-indri node onto ringtail k3s, shedding ~1.1 GiB of resident load. Second chain in the indri-k8s decommission after immich.

**Containers ported to Nix (default.nix), build-verified on ringtail:**
- paperless → wraps nixpkgs paperless-ngx 2.20.15 (pinned unstable); runs as web/worker/beat/consumer
- mealie → wraps nixpkgs mealie 3.16.0 (forward 4-minor bump, breaking-change reviewed); single gunicorn, SQLite
- teslamate → from-scratch beamPackages mixRelease (not in nixpkgs); erlang_27+elixir_1_18, npm assets, ex_cldr locales pre-fetched

**Data:** cold downtime-tolerant cutover. paperless+teslamate postgres dump/restore from quiesced source into a new ringtail blumeops-pg CNPG cluster; mealie SQLite PVC copied. Source DBs untouched until verified (rollback = repoint).

**Also:** ringtail blumeops-pg cluster + ExternalSecrets scaffold; fixes pre-existing shower version-check drift.

Runbook: docs/how-to/ringtail/migrate-wave1-ringtail.md. Deploy-from-branch + cutover happens before merge; container images rebuilt from main after merge.
Reviewed-on: #363

argocd/manifests/paperless-ringtail/service.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: paperless
+  namespace: paperless
+spec:
+  selector:
+    app: paperless
+  ports:
+    - name: http
+      port: 8000
+      targetPort: 8000
+      protocol: TCP