fix(windows): dismiss the overlay when any new window opens
The Windows switcher is alwaysOnTop overlay-role; without an
auto-dismiss path, hitting cmd+n (or any other shortcut/cmd that
spawns a window) opened the new window *behind* the switcher,
leaving the user staring at a stale overlay.
Subscribes the windows-overlay tile to `window:opened` (which
ipc.ts publishes whenever any tile-launched or page-host window
is created) and self-closes via window.close(). The existing
overlay close handler restores hidden windows and applies the
post-overlay focus target, so the just-opened window ends up
focused as expected.
Self-creation is filtered by comparing msg.id against our own
api.window.getInfo().id.