BusyMirror 1.3.9 - 2026-04-09

Changes
- Add a menu bar extra with `Sync Now`, `Open BusyMirror`, and `Quit BusyMirror`.
- Route menu bar sync requests through the same mirroring flow as the main window, opening the window automatically when needed.
- Run BusyMirror as a menu bar-only app so it no longer appears in the Dock.

Build
- Version bump to 1.3.9 (build 17).
