Regenerate App

Regenerate an app's bundle independently (without running finalize_steps).

Runs on the branch the caller NAMES, or — for a client that names none — on their default work branch, auto-forked on first use. Never on main: landing-only main admits no exception for the no-chat dispatch path, because a regenerate that wrote straight to main would put one editor's unreviewed build on the trunk while everyone else's branches sat behind it.