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/volume_readout_test.dart

@@ -0,0 +1,97 @@
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:media_kit/media_kit.dart';
+import 'package:media_kit_video/media_kit_video.dart' show VideoState;
+import 'package:watch_together/src/controls/model/controls_prefs.dart';
+import 'package:watch_together/src/controls/frame.dart';
+import 'package:watch_together/src/shell/session_player.dart';
+import 'package:watch_together/src/state/session_state.dart';
+import 'package:watch_together/src/state/settings.dart';
+
+// The wheel anywhere on the full player flashes the volume readout, in
+// both skins, windowed and fullscreen, with the controls up or hidden.
+// The picture is a black box with the session's controls on it (never a
+// media_kit `Video`).
+
+void main() {
+  final coord = SessionState.instance.coordinator;
+  final s = AppSettings.instance;
+
+  // A real player for the volume steps to go to. Never disposed: the
+  // steps' mpv calls start in the test's fake time and never finish, so a
+  // dispose would wait on them for ever; the test process ending ends it.
+  setUpAll(() async {
+    MediaKit.ensureInitialized();
+    await coord.playback.init();
+  });
+
+  testWidgets('wheel over the video: readout for about a second', (tester) async {
+    addTearDown(() => s.controlsSkin.value = ControlsSkin.standard);
+    tester.view.physicalSize = const Size(1280, 720);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.reset);
+
+    final readout = find.byKey(const ValueKey('volume-readout'));
+    double opacity() => readout.evaluate().isEmpty
+        ? 0
+        : tester.widget<AnimatedOpacity>(find.ancestor(of: readout, matching: find.byType(AnimatedOpacity)).first).opacity;
+    Future<void> wheel() async {
+      await tester.sendEventToBinding(
+          PointerScrollEvent(kind: PointerDeviceKind.mouse, position: const Offset(640, 300), scrollDelta: const Offset(0, -60)));
+      await tester.pump();
+    }
+
+    for (final skin in ControlsSkin.values) {
+      for (final fullscreen in [false, true]) {
+        final what = '${skin.name}, ${fullscreen ? 'fullscreen' : 'windowed'}';
+        s.controlsSkin.value = skin;
+        await tester.pumpWidget(MaterialApp(
+          theme: ThemeData.dark(),
+          home: Scaffold(
+            body: SessionPlayer(
+              key: ValueKey(what),
+              mode: PlayerMode.full,
+              fullscreen: fullscreen,
+              onExpand: () {},
+              onCollapse: () {},
+              onClose: () {},
+              onToggleFullscreen: () {},
+              onToggleChat: () {},
+              onChangeVideo: () {},
+              onOpenIntegrations: () {},
+              onLeave: () {},
+              windowControls: false,
+              videoBuilder: (context, controls) => Stack(fit: StackFit.expand, children: [
+                const ColoredBox(color: Colors.black),
+                if (controls != null) controls(VideoState()),
+              ]),
+            ),
+          ),
+        ));
+        await tester.pump();
+        expect(opacity(), 0, reason: '$what: nothing before a step');
+
+        // Controls up.
+        expect(tester.state<ControlsFrameState>(find.byType(ControlsFrame)).visible, isTrue, reason: what);
+        await wheel();
+        expect(opacity(), 1, reason: '$what, controls up: shown');
+        await tester.pump(const Duration(milliseconds: 900));
+        expect(opacity(), 1, reason: '$what: still up within the second');
+        await tester.pump(const Duration(milliseconds: 300));
+        expect(opacity(), 0, reason: '$what: gone after the second');
+
+        // Controls hidden (no mouse movement past the hide delay).
+        await tester.pump(Duration(seconds: s.controlsHideSecs.value + 1));
+        await tester.pump(const Duration(milliseconds: 500));
+        expect(tester.state<ControlsFrameState>(find.byType(ControlsFrame)).visible, isFalse, reason: what);
+        await wheel();
+        expect(opacity(), 1, reason: '$what, controls hidden: shown');
+        await tester.pump(const Duration(milliseconds: 1200));
+        expect(opacity(), 0, reason: '$what: gone after the second');
+      }
+    }
+    await tester.pumpWidget(const SizedBox());
+    await tester.pump(const Duration(seconds: 5));
+  });
+}