fix(ulw-loop): report a differing driver objective once and keep create_goal advice for a missing driver (refs #8333)

reconcileCodexGoalSnapshot now returns nextActions (create, re-create, or
resume the driver goal) separately from warnings (a differing objective),
so the informational text never masquerades as an action. The first
checkpoint or review-blockers record under a differing driver acknowledges
the objective in plan.acknowledgedDriverObjectives (steering-protected) and
later calls stay quiet; a driver rewritten to a third objective is reported
again. SDK envelopes lift result.warnings beside nextActions.