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/linux/CMakeLists.txt

@@ -4,10 +4,10 @@ project(runner LANGUAGES CXX)
 
 # The name of the executable created for the application. Change this to change
 # the on-disk name of your application.
-set(BINARY_NAME "watch_together")
+set(BINARY_NAME "starsync")
 # The unique GTK application identifier for this application. See:
 # https://wiki.gnome.org/HowDoI/ChooseApplicationID
-set(APPLICATION_ID "moe.senkochan.watch_together")
+set(APPLICATION_ID "dev.foxyz.starsync")
 
 # Explicitly opt in to modern CMake behaviors to avoid warnings with recent
 # versions of CMake.