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/scripts/bt-service

@@ -48,6 +48,10 @@ run_action() {
         collector-off)
             systemctl disable --now buttontask-collector
             ;;
+        bluez-restart)
+            # Called by the collector when bluetoothd stops answering D-Bus.
+            systemctl restart bluetooth
+            ;;
         units)
             systemctl list-units --type=service --all --no-legend --plain --no-pager \
                 || systemctl list-units --type=service --all --no-legend --no-pager
@@ -60,7 +64,7 @@ run_action() {
             emit_journal
             ;;
         *)
-            echo "usage: bt-service {start|stop|restart|collector-on|collector-off|units|journal}" >&2
+            echo "usage: bt-service {start|stop|restart|collector-on|collector-off|bluez-restart|units|journal}" >&2
             exit 2
             ;;
     esac