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/jellyfin_e2e_test.dart

@@ -501,7 +501,8 @@ void main() {
         expect(a.jellyfinPlan.peek(), isA<OwnPlay>());
         expect(a.relaying.peek(), isTrue);
         expect(b.jellyfinBlocked.peek(), isNull);
-        for (final x in [a, b]) {
+        // Everyone present counts for the gate, Dave too.
+        for (final x in [a, b, d]) {
           x.toggleReady();
         }
         await _poll(() => a.playback.player.state.playing && b.playback.player.state.playing, 'playing');
@@ -511,7 +512,7 @@ void main() {
         expect(jelly.streams('ATOKEN'), isNotEmpty);
         expect(jelly.calls.where((c) => c.path.startsWith('/Videos/')).every((c) =>
             _FakeJellyfin.authFields(c.auth)['Token'] == 'ATOKEN'), isTrue);
-        for (final x in [a, b]) {
+        for (final x in [a, b, d]) {
           x.toggleReady();
         }