collector: survive bluetoothd hangs and restarts

- every BlueZ call runs off the asyncio thread with a timeout; if bluetoothd
  stays unresponsive for 30 s the collector restarts bluetooth.service and
  exits for a clean re-registration
- Type=notify + WatchdogSec for buttontask-collector, never give up restarting
- bluetooth.service drop-in: Restart=always (BlueZ 5.55 crashes on assert/SEGV),
  installed by device-install.sh and OTA (bt-update)
- bt-service: bluez-restart action for the collector

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

webconfig/buttontask-collector.service

@@ -2,9 +2,17 @@
 Description=ButtonTask BLE Sensor Collector
 After=bluetooth.service dbus.service
 Wants=bluetooth.service
+# Never give up restarting: the collector exits on purpose whenever
+# bluetoothd restarts or hangs, to re-register GATT/advertising from scratch.
+StartLimitIntervalSec=0
 
 [Service]
-Type=simple
+# Type=notify + watchdog: the collector sends READY=1 after GATT start and
+# WATCHDOG=1 every loop tick; a stuck event loop gets killed and restarted.
+Type=notify
+NotifyAccess=main
+WatchdogSec=60
+TimeoutStartSec=90
 User=buttontask
 Group=buttontask
 SupplementaryGroups=bluetooth
@@ -12,7 +20,7 @@ WorkingDirectory=/opt/buttontask/current/collector
 Environment=BUTTONTASK_ROOT=/opt/buttontask
 Environment=PYTHONUNBUFFERED=1
 ExecStart=/usr/bin/python3 /opt/buttontask/current/collector/main.py
-Restart=on-failure
+Restart=always
 RestartSec=3
 
 [Install]