fix(gui): honest key setup outcomes, quit confirmation, streamer mode leaks

[timhartmann7]

• Key setup asks first, names the key file it creates, and focuses Cancel.
• Key setup without passwordless sudo says password login is still on and keeps the saved password, in both apps; the card shows "Password on" with a re-run, and a shield for key-only hosts.
• A late key setup failure says whether password login was restored or may still be off, saves the tested key, and explains how to check and restore; a failed rollback is no longer reported as restored.
• Closing the window, ⌘Q and the tray's Quit ask while terminals, transfers, tunnels or snippet runs are open, with "Don't ask again" and a Settings switch; a hung or crashed page can't block closing.
• On macOS ⌘W closes the active tab and ⌘⇧W the window.
• Streamer mode masks addresses in error text and the host form, shows an eye in the status bar, and toggles from the palette or ⌘⇧S / Ctrl+Shift+S.