Operations and observability for sifaka NAS (#135)

## Summary
- Add `smartctl_exporter` Docker container to sifaka for SMART disk health monitoring
- Formalize existing `node_exporter` container under Ansible management
- Route both exporters through Caddy L4 TCP proxy (`nas.ops.eblu.me:9100`, `nas.ops.eblu.me:9633`), replacing the hardcoded LAN IP in Prometheus
- Create "Sifaka Disk Health" Grafana dashboard (health status, temperature, wear indicators, lifetime)
- Introduce `ansible/playbooks/sifaka.yml` and `mise run provision-sifaka` — first Ansible playbook for the NAS
- Shared exporter port variables in `group_vars/all.yml` to avoid duplication between Caddy and sifaka roles

## Prerequisites before deploy
- [ ] Enable SSH on sifaka (DSM Control Panel > Terminal & SNMP)
- [ ] Verify `ssh eblume@sifaka 'docker ps'` works
- [ ] Run `mise run provision-sifaka` to deploy containers
- [ ] Run `mise run provision-indri -- --tags caddy` to add L4 routes
- [ ] `argocd app sync prometheus` + `argocd app sync grafana-config`

## Test plan
- [ ] Verify smartctl_exporter metrics: `curl http://nas.ops.eblu.me:9633/metrics`
- [ ] Verify Prometheus targets page shows both sifaka jobs as UP
- [ ] Verify Grafana "Sifaka Disk Health" dashboard loads with data

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/135

ansible/roles/caddy/defaults/main.yml

@@ -84,3 +84,7 @@ caddy_tcp_services:
     backend: "localhost:2200"  # Forgejo SSH
   - port: 5432
     backend: "pg.tail8d86e.ts.net:5432"  # PostgreSQL
+  - port: "{{ sifaka_node_exporter_port }}"
+    backend: "sifaka:{{ sifaka_node_exporter_port }}"  # Sifaka node_exporter
+  - port: "{{ sifaka_smartctl_exporter_port }}"
+    backend: "sifaka:{{ sifaka_smartctl_exporter_port }}"  # Sifaka smartctl_exporter