feat(media): add Immich photo/video management service

- Add immich_server, immich_ml, and immich_postgres services
- Use dedicated PostgreSQL with vector extensions (vectorchord + pgvectors)
- Connect to core Redis for job queues
- Configure Traefik routing for immich.media.pivoine.art
- Add backup volumes and plan for Backrest (daily at 12:00)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

core/backrest/config.json

@@ -346,6 +346,25 @@
           "yearly": 3
         }
       }
+    },
+    {
+      "id": "immich-backup",
+      "repo": "hidrive-backup",
+      "paths": [
+        "/volumes/immich_postgres_data",
+        "/volumes/immich_upload"
+      ],
+      "schedule": {
+        "cron": "0 12 * * *"
+      },
+      "retention": {
+        "policyTimeBucketed": {
+          "daily": 7,
+          "weekly": 4,
+          "monthly": 6,
+          "yearly": 2
+        }
+      }
     }
   ]
 }