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/shell/settings_tab.dart

@@ -79,7 +79,23 @@ class SettingsTab extends StatelessWidget {
           ),
         ];
       case SettingsSection.network:
-        return const [HostDefaultsPanel(), RecentServersPanel()];
+        return [
+          const HostDefaultsPanel(),
+          const RecentServersPanel(),
+          SettingsPanel(
+            title: 'Watching',
+            child: SignalBuilder(
+              builder: (context) => SwitchListTile(
+                key: const ValueKey('unready-on-swap'),
+                contentPadding: EdgeInsets.zero,
+                title: const Text('Unready when the video changes'),
+                subtitle: const Text('Otherwise you stay ready and the next video starts once everyone ready has buffered'),
+                value: AppSettings.instance.unreadyOnSwap.value,
+                onChanged: AppSettings.instance.setUnreadyOnSwap,
+              ),
+            ),
+          ),
+        ];
       case SettingsSection.player:
         return [
           const SettingsHintCard(