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/lib/src/widgets/app_keys.dart

@@ -0,0 +1,101 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+import '../state/session_state.dart';
+import 'text_focus.dart';
+
+/// Tab and Shift+Tab never move focus (the app's [Shortcuts] override):
+/// a button that got focus that way would be pressed by Space, the ready
+/// key.
+Map<ShortcutActivator, Intent> get appShortcuts => {
+      ...WidgetsApp.defaultShortcuts,
+      const SingleActivator(LogicalKeyboardKey.tab): const DoNothingIntent(),
+      const SingleActivator(LogicalKeyboardKey.tab, shift: true): const DoNothingIntent(),
+    };
+
+/// The window's two app-wide keys, ahead of whatever has focus: while in a
+/// server, Space is ready / not ready and Tab opens or closes the chat,
+/// on every tab and in every player mode. Not while a text field has
+/// focus (the chat field handles Tab and Esc itself) nor while a dialog or
+/// menu is in front of [child].
+class AppKeys extends StatefulWidget {
+  /// Who toggles the chat, latest first: the strip while it is shown, the
+  /// full player in fullscreen (both hold the shell's toggle).
+  static final _chatToggles = <VoidCallback>[];
+
+  static void addChatToggle(VoidCallback f) => _chatToggles.add(f);
+  static void removeChatToggle(VoidCallback f) => _chatToggles.remove(f);
+
+  /// Space; tests count presses instead of sending them.
+  final VoidCallback? onToggleReady;
+  final Widget child;
+  const AppKeys({super.key, this.onToggleReady, required this.child});
+
+  @override
+  State<AppKeys> createState() => _AppKeysState();
+}
+
+class _AppKeysState extends State<AppKeys> {
+  @override
+  void initState() {
+    super.initState();
+    HardwareKeyboard.instance.addHandler(_key);
+  }
+
+  @override
+  void dispose() {
+    HardwareKeyboard.instance.removeHandler(_key);
+    super.dispose();
+  }
+
+  bool _key(KeyEvent event) {
+    if (event is! KeyDownEvent || !mounted) return false;
+    final key = event.logicalKey;
+    if (key != LogicalKeyboardKey.space && key != LogicalKeyboardKey.tab) return false;
+    if (SessionState.instance.route.peek() != AppRoute.session) return false;
+    if (ModalRoute.of(context)?.isCurrent == false) return false;
+    if (textInputFocused()) return false;
+    final keys = HardwareKeyboard.instance;
+    if (keys.isControlPressed || keys.isAltPressed || keys.isMetaPressed) return false;
+    if (key == LogicalKeyboardKey.space) {
+      (widget.onToggleReady ?? SessionState.instance.coordinator.toggleReady)();
+      return true;
+    }
+    final toggles = AppKeys._chatToggles;
+    if (toggles.isEmpty) return false;
+    toggles.last();
+    return true;
+  }
+
+  @override
+  Widget build(BuildContext context) => widget.child;
+}
+
+/// Registers [onToggle] with [AppKeys] while mounted.
+class ChatKey extends StatefulWidget {
+  final VoidCallback onToggle;
+  final Widget child;
+  const ChatKey({super.key, required this.onToggle, required this.child});
+
+  @override
+  State<ChatKey> createState() => _ChatKeyState();
+}
+
+class _ChatKeyState extends State<ChatKey> {
+  void _toggle() => widget.onToggle();
+
+  @override
+  void initState() {
+    super.initState();
+    AppKeys.addChatToggle(_toggle);
+  }
+
+  @override
+  void dispose() {
+    AppKeys.removeChatToggle(_toggle);
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) => widget.child;
+}