- tray icon and tooltip now reflect engine state: grey when stopped,
green + live frame/drop counters in the tooltip while streaming
- generate a proper app icon (assets/, via cmd/teleportfling-icon) and
embed it so the window and tray carry the icon without runtime files
- add a .desktop entry template for launching from an app menu
- run Fyne UI updates (status label, tray icon/tooltip) on the main
thread via fyne.Do to satisfy the threading model