refactor: drive UI from service signals, drop redundant polling

- bluetooth.py / wifi.py: remove 5s periodic refresh timers; rely on
  service `changed`/`device-added`/`device-removed`/`notify` signals
- expanded_player.py: remove 500ms metadata poll; rely on
  `meta-change`/`artwork-change` signals
- player.py (notch): connect previously dangling `artwork-change` handler
- popup_win.py: silence harmless "nothing connected" warning on destroy()

No behaviour change; eliminates dead timers and log spam.

src/window/panel/notch/player.py

@@ -137,6 +137,7 @@ class NotchPlayer(Box):
         self._update_from_service()
         self._sigs.append(service.connect("play", self._on_play))
         self._sigs.append(service.connect("pause", self._on_pause))
+        self._sigs.append(service.connect("artwork-change", self._on_artwork_change))
 
         if service.playback_status == "Playing":
             self._start_timer()