Restructure step R: the app is Starsync (dev.foxyz.starsync)

- Linux app id dev.foxyz.starsync, binary starsync; Windows starsync.exe,
  company foxyz; server starsync-server; Dart package starsync; archives
  starsync-<ver>-*.
- 1.2.x compatibility: watch_together and watch-together-server
  launchers (Linux) / copies (Windows) in the archive; the updater
  accepts both names and relaunches the new binary; update.sh/.bat use
  whichever server exists.
- First start copies (never moves) the old support folder and this
  app's Hive boxes out of ~/Documents into <support>/hive; a marker
  makes it run once; AppDirs is a port; settings schema version with
  ordered migrations.
- Launcher entry dev.foxyz.starsync.desktop; the old one removed.
- Repository name and URLs unchanged.

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

apps/desktop/lib/main.dart

@@ -7,9 +7,9 @@ import 'package:media_kit/media_kit.dart';
 import 'package:sync_relay_core/core.dart';
 
 import 'app.dart';
-import 'src/platform/app_dirs.dart';
 import 'src/platform/app_log.dart';
 import 'src/platform/app_shutdown.dart';
+import 'src/platform/desktop/desktop_app_dirs.dart';
 import 'src/platform/desktop_entry.dart';
 import 'src/screens/home/ui.dart';
 import 'src/session/app_events.dart' show UpdateAvailable;
@@ -42,10 +42,9 @@ Future<void> main(List<String> args) async {
         ),
       );
   WidgetsFlutterBinding.ensureInitialized();
-  final dirs = await AppDirs.resolve();
+  final dirs = await const DesktopAppDirs().resolve();
   await startAppLogging(dirs);
-  // An absolute subDir replaces the documents folder (package:path join).
-  await Hive.initFlutter(dirs.hive);
+  Hive.init(dirs.hive);
   await AppSettings.instance.ensureLoaded();
   // Close button / Alt+F4: the orderly close ([shutDownApp]), so others
   // see "left", a hosted server shuts down and no player outlives the