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/test/update_controller_test.dart

@@ -205,6 +205,26 @@ void main() {
       expect(dev.status.value.phase, UpdatePhase.idle);
     });
 
+    test('Later hides it until the next check; a check leaves an install be',
+        () async {
+      final c = UpdateController(
+          currentVersion: '0.1.0',
+          manifestUrl: server.manifestUrl,
+          executablePath: '${work.path}/stray-binary',
+          restart: (_, _) async {});
+      await c.checkOnce();
+      expect(c.status.value.phase, UpdatePhase.available);
+      c.dismiss();
+      expect(c.status.value.phase, UpdatePhase.idle);
+      await c.checkNow();
+      expect(c.status.value.phase, UpdatePhase.available);
+      final m = c.status.value.manifest;
+      c.status.value = UpdateStatus(UpdatePhase.downloading,
+          manifest: m, progress: 0.4, canInstall: true);
+      await c.checkNow();
+      expect(c.status.value.phase, UpdatePhase.downloading);
+    });
+
     test('failed install shows error, install untouched, retry works',
         () async {
       server.manifestExtra = {'sha256': '0' * 64};