Approve & Merge is now the only review+merge entry. For a parent with
children it drives the unit merge via the worker (conflicts still surface
through the existing PlanningMergeConflict dialog); the separate Merge All
Subtasks button, MergeAllCommand, CanMergeAll plumbing, and the dead
MergeAllPlanningAsync client method are removed. Combined-diff preview and
conflict continue/abort are kept.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Add a StubWorkerClient base implementing the full IWorkerClient surface so
the planning/conflict/diff test fakes only override the members they exercise.
Eliminates the constructor-drift duplication across the three fakes.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
