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/handoff_test.dart

@@ -0,0 +1,46 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:watch_together/src/shell/handoff.dart';
+
+// What a drop or a paste is: decided from paths and text alone (the file
+// system stands behind a fake).
+
+void main() {
+  const fs = {
+    '/v/a.mkv': FileSystemEntityType.file,
+    '/v/b.MP4': FileSystemEntityType.file,
+    '/v/notes.txt': FileSystemEntityType.file,
+    '/v/cover.jpg': FileSystemEntityType.file,
+    '/v/Season 1': FileSystemEntityType.directory,
+    '/v/folder.mkv': FileSystemEntityType.directory,
+    r'C:\Videos\c.mkv': FileSystemEntityType.file,
+  };
+  Handoff of({List<String> paths = const [], String? text}) =>
+      classifyHandoff(paths: paths, text: text, typeOf: (p) => fs[p] ?? FileSystemEntityType.notFound);
+
+  test('videos by extension, in order; others dropped with them are left out', () {
+    final h = of(paths: ['/v/notes.txt', '/v/b.MP4', '/v/Season 1', '/v/a.mkv']);
+    expect((h as HandoffVideos).paths, ['/v/b.MP4', '/v/a.mkv']);
+  });
+
+  test('a folder (even one named like a video), else an image, else nothing', () {
+    expect((of(paths: ['/v/notes.txt', '/v/folder.mkv']) as HandoffFolder).path, '/v/folder.mkv');
+    expect((of(paths: ['/v/cover.jpg']) as HandoffImage).path, '/v/cover.jpg');
+    expect(of(paths: ['/v/notes.txt']), isA<HandoffNothing>());
+    expect(of(paths: ['/gone/x.mkv']), isA<HandoffNothing>());
+    expect(of(), isA<HandoffNothing>());
+  });
+
+  test('pasted text: a link, absolute paths or file URIs; files win over text', () {
+    expect(of(text: '  https://cdn.example/a b'), isA<HandoffNothing>());
+    expect((of(text: ' https://youtu.be/x?t=1 \n') as HandoffLink).url, 'https://youtu.be/x?t=1');
+    expect((of(text: 'HTTP://x.example/v.mp4') as HandoffLink).url, 'HTTP://x.example/v.mp4');
+    expect((of(text: '/v/a.mkv\n/v/b.MP4') as HandoffVideos).paths, ['/v/a.mkv', '/v/b.MP4']);
+    expect((of(text: 'file:///v/Season%201') as HandoffFolder).path, '/v/Season 1');
+    expect((of(text: r'C:\Videos\c.mkv') as HandoffVideos).paths, [r'C:\Videos\c.mkv']);
+    expect(of(text: 'v/a.mkv'), isA<HandoffNothing>(), reason: 'relative');
+    expect(of(text: 'hello'), isA<HandoffNothing>());
+    expect((of(paths: ['/v/Season 1'], text: 'https://x.example') as HandoffFolder).path, '/v/Season 1');
+  });
+}