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/test/ytdl_headers_e2e_test.dart

@@ -3,7 +3,7 @@ import 'dart:io';
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:media_kit/media_kit.dart';
-import 'package:watch_together/src/playback/playback_controller.dart';
+import 'package:starsync/src/playback/playback_controller.dart';
 
 final _tmp = Platform.environment['WT_TEST_TMP'] ?? Directory.systemTemp.path;
 const _referer = 'https://www.bilibili.com/';