docs: update DEPLOYMENT.md and C4 diagram for observability scaffold

Replace the stale "no monitoring infrastructure in place yet" note in
§4 with a brief description of the observability compose file and a
pointer to issue #581 for full docs.

Add a placeholder System_Boundary block for Prometheus + Loki + Grafana
to l2-containers.puml, showing the stack joins archiv-net.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/DEPLOYMENT.md

@@ -256,9 +256,9 @@ docker compose logs --tail=200 <service>
 - **Spring Actuator health**: `http://localhost:8080/actuator/health` (internal only in prod — port 8081 for Prometheus scraping)
 - **Prometheus scraping**: management port 8081, path `/actuator/prometheus`. Internal only; Caddy blocks `/actuator/*` externally.
 
-### Future observability
+### Observability stack
 
-Phase 7 of the Production v1 milestone adds Prometheus + Loki + Grafana. No monitoring infrastructure is in place yet.
+An observability stack (Prometheus + Loki + Grafana) is available via `docker-compose.observability.yml` and configuration lives under `infra/observability/`. It joins the `archiv-net` Docker network to scrape the backend's management port. Full wiring and runbook documentation is tracked in issue #581.
 
 ---
 

docs/architecture/c4/l2-containers.puml

@@ -17,6 +17,12 @@ System_Boundary(archiv, "Familienarchiv (Docker Compose)") {
     Container(mc, "Bucket / Service-Account Init", "MinIO Client (mc)", "One-shot container on startup. Idempotent: creates the archive bucket, the archiv-app service account, and attaches the readwrite policy.")
 }
 
+System_Boundary(observability, "Observability Stack (docker-compose.observability.yml / archiv-net)") {
+    Container(prometheus, "Prometheus", "prom/prometheus", "Scrapes metrics from backend management port 8081 (/actuator/prometheus). Retention and alert rules TBD — see issue #581.")
+    Container(loki, "Loki", "grafana/loki", "Log aggregation. Receives structured logs from the stack. Wiring TBD — see issue #581.")
+    Container(grafana, "Grafana", "grafana/grafana", "Dashboards and alerting UI. Data sources: Prometheus + Loki. Wiring TBD — see issue #581.")
+}
+
 Rel(user, caddy, "HTTPS", "TLS 1.2/1.3")
 Rel(caddy, frontend, "Reverse proxies non-/api requests", "HTTP / loopback:3000")
 Rel(caddy, backend, "Reverse proxies /api/*", "HTTP / loopback:8080")