Lift the submit orchestration out of ChatBar into
composer/hooks/use-composer-submit.ts: `submitDraft` (the one decision tree —
queue-edit save · slash-now-while-busy · queue · drain · send · stop),
`dispatchSubmit` (the shared send-with-restore primitive + the external-submit
listener), and `steerDraft`.
This is the seam where the draft and queue engines meet; it now reads both clean
APIs as explicit inputs instead of closing over inline state. ChatBar is left as
a thin coordinator that owns the shared `queueEditRef` and wires the four engines
(draft · queue · submit · metrics/voice/drop) into render.
Behaviour-identical (verbatim move). Verified: typecheck clean, composer DOM
repro tests (enter-submit, IME, slash-now, steer, drain) pass.