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/desktop_entry_test.dart

@@ -0,0 +1,37 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:starsync/src/platform/desktop_entry.dart';
+
+void main() {
+  test('writes the Starsync entry, removes only the old id\'s files', () async {
+    final tmp = await Directory.systemTemp.createTemp('starsync-entry');
+    try {
+      final root = '${tmp.path}/install';
+      await Directory('$root/lib').create(recursive: true);
+      await Directory('$root/data/flutter_assets/assets/icon').create(recursive: true);
+      await File('$root/data/flutter_assets/assets/icon/icon_48.png').writeAsString('png');
+      final share = '${tmp.path}/share';
+      final apps = Directory('$share/applications')..createSync(recursive: true);
+      final oldEntry = File('${apps.path}/$legacyAppId.desktop')..writeAsStringSync('old');
+      final other = File('${apps.path}/other.app.desktop')..writeAsStringSync('keep');
+      final oldIcon = File('$share/icons/hicolor/48x48/apps/$legacyAppId.png')
+        ..createSync(recursive: true);
+      final otherIcon = File('$share/icons/hicolor/48x48/apps/other.png')..createSync();
+
+      await installDesktopEntry(executable: '$root/starsync', dataHome: share, force: true);
+
+      expect(oldEntry.existsSync(), isFalse);
+      expect(oldIcon.existsSync(), isFalse);
+      expect(other.existsSync(), isTrue);
+      expect(otherIcon.existsSync(), isTrue);
+      final entry = File('${apps.path}/dev.foxyz.starsync.desktop').readAsStringSync();
+      expect(entry, contains('Exec="$root/starsync"'));
+      expect(entry, contains('StartupWMClass=dev.foxyz.starsync'));
+      expect(entry, contains('Icon=dev.foxyz.starsync'));
+      expect(File('$share/icons/hicolor/48x48/apps/dev.foxyz.starsync.png').existsSync(), isTrue);
+    } finally {
+      await tmp.delete(recursive: true);
+    }
+  }, skip: Platform.isLinux ? null : 'Linux launcher entry');
+}