feat: crash recovery, service_failed monitoring, broker health fields, command expiry sweep

- Add GET /api/clients/crashed endpoint (process_status=crashed or stale heartbeat)
- Add restart_app command action with same lifecycle + lockout as reboot_host
- Scheduler: crash auto-recovery loop (CRASH_RECOVERY_ENABLED flag, lockout, MQTT publish)
- Scheduler: unconditional command expiry sweep per poll cycle (sweep_expired_commands)
- Listener: subscribe to infoscreen/+/service_failed; persist service_failed_at + unit
- Listener: extract broker_connection block from health payload; persist reconnect_count + last_disconnect_at
- DB migration b1c2d3e4f5a6: service_failed_at, service_failed_unit, mqtt_reconnect_count, mqtt_last_disconnect_at on clients
- Add GET /api/clients/service_failed and POST /api/clients/<uuid>/clear_service_failed
- Monitoring overview API: include mqtt_reconnect_count + mqtt_last_disconnect_at per client
- Frontend: orange service-failed alert panel (hidden when empty, auto-refresh, quittieren action)
- Frontend: MQTT reconnect count + last disconnect in client detail panel
- MQTT auth hardening: listener/scheduler/server use env credentials; broker enforces allow_anonymous false
- Client command lifecycle foundation: ClientCommand model, reboot_host/shutdown_host, full ACK lifecycle
- Docs: TECH-CHANGELOG, DEV-CHANGELOG, MQTT_EVENT_PAYLOAD_GUIDE, copilot-instructions updated
- Add implementation-plans/, RESTART_VALIDATION_CHECKLIST.md, TODO.md

.env.example

@@ -20,8 +20,18 @@ DB_HOST=db
 # MQTT
 MQTT_BROKER_HOST=mqtt
 MQTT_BROKER_PORT=1883
-# MQTT_USER=your_mqtt_user
-# MQTT_PASSWORD=your_mqtt_password
+# Required for authenticated broker access
+MQTT_USER=your_mqtt_user
+MQTT_PASSWORD=replace_with_a_32plus_char_random_password
+# Optional: dedicated canary client account
+MQTT_CANARY_USER=your_canary_mqtt_user
+MQTT_CANARY_PASSWORD=replace_with_a_different_32plus_char_random_password
+# Optional TLS settings
+MQTT_TLS_ENABLED=false
+MQTT_TLS_CA_CERT=
+MQTT_TLS_CERTFILE=
+MQTT_TLS_KEYFILE=
+MQTT_TLS_INSECURE=false
 MQTT_KEEPALIVE=60
 
 # Dashboard
@@ -39,6 +49,12 @@ HEARTBEAT_GRACE_PERIOD_PROD=170
 # Optional: force periodic republish even without changes
 # REFRESH_SECONDS=0
 
+# Crash recovery (scheduler auto-recovery)
+# CRASH_RECOVERY_ENABLED=false
+# CRASH_RECOVERY_GRACE_SECONDS=180
+# CRASH_RECOVERY_LOCKOUT_MINUTES=15
+# CRASH_RECOVERY_COMMAND_EXPIRY_SECONDS=240
+
 # Default superadmin bootstrap (server/init_defaults.py)
 # REQUIRED: Must be set for superadmin creation
 DEFAULT_SUPERADMIN_USERNAME=superadmin