Restructure step 3: your server, Invite, version gate, AppGraph

- One server per app run (loopback, no password); Invite attaches an
  all-interfaces listener to the same server and Stop sharing detaches
  it (guests told with 4016); members, media and Up next never reset.
  No solo mode: you're home on your own server unless in a friend's.
- Navigation: none / yours / friend; a join passes a version gate on
  /health first (clear "they/you need to update", update offer).
- Invite as a value (host, port, name, password flag, version, fp
  reserved); addresses filtered (loopback, link-local, 198.18/15,
  bridges) and ranked; Sharing chip, Copy invite, Stop sharing.
- Alone looks like a plain player (alone replaces solo).
- AppGraph builds and disposes systems; widgets use AppScope;
  SessionState deleted; a test caps the remaining singletons.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/jellyfin/browse_scope.dart

@@ -339,9 +339,9 @@ class BrowseScope extends InheritedWidget {
       case 2:
         queue!(item, next: true);
       case 3:
-        await copyToClipboard(jellyfinCopyTitle(item), done: 'Title copied');
+        if (context.mounted) await copyToClipboard(context, jellyfinCopyTitle(item), done: 'Title copied');
       case 4:
-        await openLink(jellyfinWebUrl(client.baseUrl, item.id, serverId: account.serverId));
+        if (context.mounted) await openLink(context, jellyfinWebUrl(client.baseUrl, item.id, serverId: account.serverId));
     }
   }