Protocol 10 presence gate, drop/paste anywhere, quick UI fixes

Ready gate: whoever is in the server while it is not playing counts (joining
while playing does not pause anyone); a swap counts everyone present and
keeps ready flags; the quorum rule is gone. Optional 'Unready when the
video changes'. No 'Skip 1:30' guess when the media has chapters.

Drag & drop and Ctrl+V anywhere (fox_utils): files, folders and links get a
small card asking how to open them. Files series start collapsed.

UI: Tab never moves focus and Space is always ready outside text fields;
chat focuses its field; unread badge on uosc and a chip in fullscreen;
people-only chat with an Activity toggle; skip pills show 5 s then with
the controls; volume up to 150%; own avatar same size as the party.

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

apps/desktop/test/app_keys_test.dart

@@ -0,0 +1,68 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:sync_relay_core/core.dart';
+import 'package:watch_together/src/shell/app_shell.dart';
+import 'package:watch_together/src/state/session_state.dart';
+import 'package:watch_together/src/update/update_controller.dart';
+import 'package:watch_together/src/widgets/app_keys.dart';
+import 'package:watch_together/src/widgets/text_focus.dart';
+
+void main() {
+  final session = SessionState.instance;
+  final coord = session.coordinator;
+
+  tearDown(() {
+    session.route.value = AppRoute.home;
+    coord.serverState.value = null;
+  });
+
+  // Regression: Tab moved focus (out of the chat field onto a button) and
+  // Space, the ready key, then pressed that button.
+  testWidgets('Tab opens and closes chat without moving focus; Space is ready', (tester) async {
+    tester.view.physicalSize = const Size(1280, 800);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.reset);
+    var readies = 0;
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData.dark(),
+      shortcuts: appShortcuts,
+      home: AppKeys(
+        onToggleReady: () => readies++,
+        child: AppShell(
+          updates: UpdateController(currentVersion: '0.0.0-dev'),
+          autoUpdateCheck: false,
+          windowControls: false,
+          videoBuilder: (context, controls) => const SizedBox(),
+        ),
+      ),
+    ));
+    coord.serverState.value = StateBroadcast(
+      eventId: 1,
+      transport: 'held',
+      position: 0,
+      serverTime: DateTime.now().toUtc(),
+      mediaId: 0,
+      members: [MemberView(id: 'a', name: 'Alex', ready: false, inSet: false, buffered: 0, stale: false)],
+    );
+    session.route.value = AppRoute.session;
+    await tester.pumpAndSettle();
+    final panel = find.byKey(const ValueKey('chat-panel'));
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+    await tester.pumpAndSettle();
+    expect(panel, findsOneWidget);
+    expect(textInputFocused(), isTrue, reason: 'opening the chat focuses its field');
+
+    // From the field: closes the chat, focus goes back, not to a button.
+    await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+    await tester.pumpAndSettle();
+    expect(panel, findsNothing);
+    expect(textInputFocused(), isFalse);
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pumpAndSettle();
+    expect(readies, 1);
+    expect(panel, findsNothing, reason: 'Space pressed a focused chat button');
+  });
+}