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/platform/app_shutdown.dart

@@ -0,0 +1,78 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:window_manager/window_manager.dart';
+
+import '../files/thumbnails.dart';
+import '../state/session_state.dart';
+import 'window_memory.dart';
+
+// The one way out of the app (close button, Alt+F4, Update and restart).
+// Order matters: every mpv player goes before the engine does (a live one
+// calls a dead Dart callback), then the network goodbye, then the window
+// closes through the platform's normal path so the engine is torn down
+// inside the message loop. The runners end the process right after
+// (`linux/runner/main.cc`, `windows/runner/main.cpp`).
+
+/// Saved on the way out; set by main once known.
+WindowMemory? shutdownWindowMemory;
+
+bool _shuttingDown = false;
+
+/// True once [shutDownApp] started.
+bool get shuttingDown => _shuttingDown;
+
+/// Hides the window, releases every player and the sound device, leaves
+/// (others see "left", a hosted server stops), runs [beforeQuit], then
+/// closes the window. Every step is bounded; a second call does nothing.
+Future<void> shutDownApp({Future<void> Function()? beforeQuit}) async {
+  if (_shuttingDown) return;
+  _shuttingDown = true;
+  final session = SessionState.instance;
+  final total = Stopwatch()..start();
+  await _step('window save', shutdownWindowMemory?.save(), const Duration(milliseconds: 500));
+  await _step('hide', windowManager.hide(), const Duration(milliseconds: 500));
+  await Future.wait([
+    _step('players', session.coordinator.releasePlayers(), const Duration(seconds: 3)),
+    _step('thumbnails', cancelAllThumbnails(), const Duration(milliseconds: 1500)),
+    _step('sounds', session.sfx.dispose(), const Duration(milliseconds: 500)),
+  ]);
+  // Windows: media_kit_video frees a player's video output on a thread of
+  // its own after dispose returns; it must be done before the engine
+  // stops, or the plugin's teardown waits on it for good.
+  if (Platform.isWindows) await Future.delayed(const Duration(milliseconds: 300));
+  // Jellyfin stop report, last diagnostics, the goodbye, then the hosted
+  // server: 3 s in all.
+  await _step('leave', session.leave(), const Duration(milliseconds: 2500));
+  await _step('server stop', session.stopServer(), const Duration(milliseconds: 500));
+  if (beforeQuit != null) await _step('before quit', beforeQuit(), const Duration(seconds: 3));
+  debugPrint('close: ready to quit after ${total.elapsedMilliseconds} ms');
+  try {
+    await windowManager.setPreventClose(false);
+    await windowManager.close();
+  } catch (e) {
+    debugPrint('window close failed: $e');
+    await windowManager.destroy();
+  }
+  // The engine stops with the window, so this only fires when the close
+  // did not go through. A kill, not exit(): no exit handlers (NVIDIA's
+  // EGL one segfaults, Windows DLL detach can hang).
+  Timer(const Duration(seconds: 3), () {
+    debugPrint('close: the window did not close; ending the process');
+    Process.killPid(pid, ProcessSignal.sigkill);
+  });
+}
+
+Future<void> _step(String what, Future<void>? f, Duration limit) async {
+  if (f == null) return;
+  final sw = Stopwatch()..start();
+  try {
+    await f.timeout(limit);
+  } on TimeoutException {
+    debugPrint('close: $what did not finish in ${limit.inMilliseconds} ms');
+  } catch (e) {
+    debugPrint('close: $what failed: $e');
+  }
+  if (sw.elapsedMilliseconds > 200) debugPrint('close: $what took ${sw.elapsedMilliseconds} ms');
+}