Adds a `toggleChat` shortcut action (default Mod+J, rebindable in
Settings -> Shortcuts) so the pop-up chat window can be opened and
dismissed without a mouse, and focuses the composer whenever the window
opens so you can start typing immediately.
The shortcut deliberately does not claim the chord where the overlay
cannot exist -- on the Chat tab, or when the Settings -> Chat preference
is off -- since flipping a hidden `isOpen` would read as a dead keypress
and then surprise the user on the next navigation. That route rule now
lives in one predicate shared with the overlay itself.
Focus is requested only on a real closed -> open transition: ChatWindow
stays mounted while closed and `isOpen` is restored from storage, so
treating mount as an open event would steal focus on page load.
Co-authored-by: Bohan-J <bohan@devv.ai>
Co-authored-by: multica-agent <github@multica.ai>