Move the keybind router out of Shell into a reusable createDispatcher
in @/utils/dispatch, covering tabs (digits 1-6, [/]), h/l depth
drill/pop + fixed-pane swipe, modes, audio transport, quit/help, and
command, delegating pane/list actions over the nav.action event bus.
Shell now renders the active page full-width with a bottom status bar
carrying the tab strip; the old sidebar pane and its leftover sidebar
action handling are removed. Adds tests covering the dispatcher's
routing behavior.
