Stabilisation quick fixes: orderly close, visible version and update band, chat pop-ups on, Windows shaders and hwdec, render logs

- Close: hide the window, dispose every player, thumbnail job and the
  sound engine, leave, then close normally; Linux runner _exit (the
  NVIDIA EGL exit handler crashed 10/10 closes, 0/41 now); Windows tears
  down inside the message loop, then TerminateProcess; watchdogs.
- Version under the Settings tab; an update band instead of a dot,
  never over a video; checks at start and every 4 hours.
- Chat pop-ups default to All again.
- Shader read-back compared as a list (old mpv joins with ','), so
  Windows stops turning shaders off; Windows hwdec auto-copy.
- Render diagnostics (`mpv: render` lines); RAM-only demuxer cache pin
  silences the file-cache warning; a volume readout test.

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

apps/desktop/lib/src/session/session_coordinator.dart

@@ -2242,6 +2242,17 @@ class SessionCoordinator {
     return 'connect failed: $e';
   }
 
+  /// App close, before [leave]: the players go first (no mpv may outlive
+  /// the engine). The Jellyfin stop report [leave] sends keeps the
+  /// position they had.
+  Future<void> releasePlayers() async {
+    if (_playerReady) _lastSnap = _snapNow();
+    _playerReady = false;
+    _ticker?.cancel();
+    _ticker = null;
+    await playback.disposeAll();
+  }
+
   Future<void> leave({bool silent = false}) async {
     _invalidateAttempts();
     await _teardown(silent: silent);