The dashboard promote route called engine.promoteBranchGroup(groupId) as a
method that never existed — only a standalone coordinator function did — so
the route was dead, masked by a vi.fn mock in the test. Add the real method on
ProjectEngine delegating to the coordinator (resolving store/cwd/settings like
attemptBranchGroupPromotion), and de-mock the test so it now fails if the
method goes missing. No PR-creation behavior yet (U5).
508b9c44d0