Prevent Seafile from Appearing in macOS Recents When Hidden from Dock

[mreid-tt]

This is a follow-up to issue #44, which introduced the option to hide the Seafile icon from the macOS dock; an excellent improvement for users who prefer a minimal interface.

However, when Seafile is launched at startup, it still appears in the "Recent Applications" section of the dock. For users who rely on the menubar icon and want to keep the dock clear, it would be helpful if either:

1. The app remains hidden from the dock entirely when no windows are open, or
2. Seafile behaves like certain background utilities: briefly appearing if interacted with, but not persisting in the recents list once closed.

This would enhance the seamless, background nature of the app for macOS users.