feat(observability): add mana-search, mana-media, and Synapse to monitoring

- Add Prometheus scraping for mana-search (port 3020, already has metrics)
- Add Prometheus scraping for mana-media (port 3015, MetricsModule added)
- Add Prometheus scraping for Matrix Synapse (port 9002, already enabled)
- Add MetricsModule to mana-media with media_ prefix
- Update Dockerfile for mana-media to include shared-nestjs-metrics
- Replace hardcoded ServiceDown alert list with dynamic regex
  (.*-backend|mana-core-auth|mana-search|mana-media|synapse)
- Replace hardcoded backends.json query with dynamic regex
- Add Search, Media, Synapse to master-overview and system-overview dashboards

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/prometheus/alerts.yml

@@ -3,7 +3,7 @@ groups:
     rules:
       # Service Down Alert
       - alert: ServiceDown
-        expr: up{job=~"mana-core-auth|chat-backend|todo-backend|calendar-backend|clock-backend|contacts-backend|storage-backend|presi-backend|nutriphi-backend|skilltree-backend|photos-backend|zitare-backend|mukke-backend|planta-backend|picture-backend"} == 0
+        expr: up{job=~"mana-core-auth|.*-backend|mana-search|mana-media|synapse"} == 0
         for: 1m
         labels:
           severity: critical

docker/prometheus/prometheus.yml

@@ -154,6 +154,31 @@ scrape_configs:
     metrics_path: '/metrics'
     scrape_interval: 30s
 
+  # ============================================
+  # Core Services
+  # ============================================
+
+  # Mana Search Service
+  - job_name: 'mana-search'
+    static_configs:
+      - targets: ['mana-search:3020']
+    metrics_path: '/metrics'
+    scrape_interval: 30s
+
+  # Mana Media Service
+  - job_name: 'mana-media'
+    static_configs:
+      - targets: ['mana-media:3015']
+    metrics_path: '/metrics'
+    scrape_interval: 30s
+
+  # Matrix Synapse
+  - job_name: 'synapse'
+    static_configs:
+      - targets: ['synapse:9002']
+    metrics_path: '/_synapse/metrics'
+    scrape_interval: 30s
+
   # ============================================
   # Pushgateway (deploy metrics, batch jobs)
   # ============================================