Remove ping_uuids from example config, update architecture diagram

- Comment out ping_uuids section in controller.yaml.example (deprecated)
- Architecture diagram: remove status.felhom.eu, update to Hub event system
- Mark Healthchecks references as deprecated throughout README

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

controller/configs/controller.yaml.example

@@ -80,12 +80,7 @@ backup:
 monitoring:
   enabled: true
   healthchecks_base: "https://status.felhom.eu"
-  ping_uuids:
-    heartbeat: ""                                  # Every 5 min — controller process alive
-    system_health: "CHANGEME-uuid-for-system-health"  # Every 5 min — comprehensive system check
-    db_dump: "CHANGEME-uuid-for-db-dump"              # Daily — after database dumps
-    backup: "CHANGEME-uuid-for-backup"                # Daily — after restic snapshot
-    backup_integrity: ""                              # Weekly (Sunday) — restic check
+  # ping_uuids: (deprecated — monitoring is now handled by the Hub event system)
   system_health_interval: "5m"
   health_check_schedule: "06:00"
   thresholds: