Harden install pipeline: health checks, log rotation, backup timer

- install.sh: Add Docker daemon check, 10GB disk space pre-flight,
  error handling on pull/up, post-startup health polling with crash
  detection, cleanup trap on failure
- docker-compose: Fix nginx/listmonk depends_on to service_healthy,
  add x-logging anchor (10m/3 files) to all ~39 services
- config.sh: Preserve existing secrets on re-run (reconfigure mode),
  add automated daily backup timer (systemd, 02:00, 30-day retention)
- mirror-images.sh: Fix gotify source tag (2.9.0 not v2.9.0)
- build-release.sh: Ensure mkdocs/docs and mkdocs/overrides dirs exist
- .env.example: Add COMPOSE_PROFILES variable

Bunker Admin

.env.example

@@ -179,6 +179,10 @@ VIDEO_PREVIEW_LINK_EXPIRY_HOURS=24
 # Leave IMAGE_TAG blank/unset (defaults to 'local') to build locally from source.
 GITEA_REGISTRY=gitea.bnkops.com/admin
 IMAGE_TAG=
+
+# Docker Compose profiles — set to 'monitoring' to include Prometheus/Grafana/Alertmanager
+# in every 'docker compose up -d'. Leave blank to start monitoring separately.
+COMPOSE_PROFILES=
 # Credentials used by the registry status API endpoint (GET /api/registry/status)
 # For docker push/pull, run: docker login gitea.bnkops.com
 GITEA_REGISTRY_USER=admin