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>

docs/HOW-IT-WORKS.md

@@ -42,7 +42,7 @@ A five-minute tour. Details: [ARCHITECTURE.md](ARCHITECTURE.md), wire format:
 
 - **Host from the app**: the app you click Host in also runs the server.
   Simplest. The server lives as long as that app.
-- **Dedicated server**: `watch-together-server`, a separate program in the
+- **Dedicated server**: `starsync-server`, a separate program in the
   release tarball, for an always-on box. See the README.
 
 Friends join either way with Join a friend in the strip at the top of the