monitoring: increase zigbee_sensor_stale threshold to 4 hours

The 2-hour threshold was too aggressive for temperature sensors in
stable environments. Historical data shows gaps up to 2.75 hours when
temperature hasn't changed (Home Assistant only updates last_updated
when values change). Increasing to 4 hours avoids false positives
while still catching genuine failures.

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

services/monitoring/rules.yml

@@ -229,13 +229,13 @@ groups:
           summary: "Mosquitto not running on {{ $labels.instance }}"
           description: "Mosquitto has been down on {{ $labels.instance }} more than 5 minutes."
       - alert: zigbee_sensor_stale
-        expr: (time() - hass_last_updated_time_seconds{entity=~"sensor\\.(0x[0-9a-f]+|temp_server)_temperature"}) > 7200
+        expr: (time() - hass_last_updated_time_seconds{entity=~"sensor\\.(0x[0-9a-f]+|temp_server)_temperature"}) > 14400
         for: 5m
         labels:
           severity: warning
         annotations:
           summary: "Zigbee sensor {{ $labels.friendly_name }} is stale"
-          description: "Zigbee temperature sensor {{ $labels.entity }} has not reported data for over 2 hours. The sensor may have a dead battery or connectivity issues."
+          description: "Zigbee temperature sensor {{ $labels.entity }} has not reported data for over 4 hours. The sensor may have a dead battery or connectivity issues."
   - name: smartctl_rules
     rules:
       - alert: smart_critical_warning