The setup launcher had no LSUIElement, and its already-installed hand-off
ran after Tauri/AppKit, whose default activation policy is Regular. That
registered the setup bundle as a second Dock app beside the real desktop.
Hand off before constructing Tauri, and restore Regular activation only
when the installer UI is actually shown.
On macOS the Electron single-instance lock also ran before deep-link
registration. setAsDefaultProtocolClient relaunches the app through Launch
Services, so the loser already had a Dock icon by the time the lock failed
and app.exit(0) ran. Register the protocol first. The lock-losing instance
still hard-exits before ready.
Fixes#73151
e726b79803