Service file and GUI separation

Changed

• Scheduled checks now run independently of the GUI
  systemd --user service units no longer depend on the Griffin Updater process (or tray) being open. Timers fire and notify-send notifications still work after the window is closed or the app is fully quit.

• Robust ExecStart resolution
  Units are generated with the best available invocation, in this order:

  1. Current AppImage path ($APPIMAGE) — the same .AppImage acts as the CLI
  2. Installed griffin-updater-cli console script
  3. python -m griffin_updater.cli (dev / editable installs)

• Main binary accepts CLI subcommands
  griffin-updater / the AppImage can now be invoked as:

  • check --id <app>
  • check-all
  • install-timers
    so systemd units can call them directly without starting the GUI.

• Changed the Icon to match the Griffin Branding

Added

• Update Scripts toolbar button
  Regenerates every service + timer for the current install method. Use after moving the AppImage, reinstalling via pip, or upgrading to 2.2.0 so existing units pick up the independent style. Shows a summary of successes/failures.