- Add `errands` table to schema with status enum and relations to agents/projects
- Add `errand` mode to agents.mode enum
- Add push rollback in orchestrator: if push fails after merge, reset to previousRef to preserve the review diff
- Extend MergeResult with previousRef for rollback support; update branch-manager and simple-git-branch-manager
- Add orchestrator tests for push rollback behaviour
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>