Add start_work.auto_commit configuration option to allow users to
disable the automatic commit step in the /start-work workflow.
When auto_commit is false:
- STEP 8: COMMIT ATOMIC UNIT is removed from orchestrator reminder
- STEP 9: PROCEED TO NEXT TASK becomes STEP 8
Resolves#2197
- Use shared OPENCODE_STORAGE, MESSAGE_STORAGE, PART_STORAGE constants
- Make isCallerOrchestrator async with SDK fallback for beta
- Fix cache implementation using Symbol sentinel
- Update atlas hooks and sisyphus-junior-notepad to use async isCallerOrchestrator