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/windows/runner/flutter_window.h

@@ -34,6 +34,9 @@ class FlutterWindow : public Win32Window {
   // "starsync/window": `attention` flashes the taskbar entry while the
   // window is not in front (lib/src/platform/attention.dart).
   std::unique_ptr<flutter::MethodChannel<flutter::EncodableValue>> window_channel_;
+
+  // The first WM_CLOSE arms the exit watchdog.
+  bool close_requested_ = false;
 };
 
 #endif  // RUNNER_FLUTTER_WINDOW_H_