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/app.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 
 import 'src/screens/home/ui.dart';
 import 'src/shell/app_shell.dart';
+import 'src/widgets/app_keys.dart';
 
 class WatchTogetherApp extends StatelessWidget {
   const WatchTogetherApp({super.key});
@@ -11,7 +12,8 @@ class WatchTogetherApp extends StatelessWidget {
     return MaterialApp(
       title: appName,
       theme: ThemeData.dark(),
-      home: const AppShell(),
+      shortcuts: appShortcuts,
+      home: const AppKeys(child: AppShell()),
     );
   }
 }