feat(safety): add Phase C advanced controls

- Add rollback manager with file checkpointing and transaction context
- Add HITL manager with approval queues and notification handlers
- Add content filter with PII, secrets, and injection detection
- Add emergency controls with stop/pause/resume capabilities
- Update SafetyConfig with checkpoint_dir setting

Issue #63

backend/app/services/safety/hitl/__init__.py

@@ -1 +1,5 @@
-"""${dir} module."""
+"""Human-in-the-Loop approval workflows."""
+
+from .manager import ApprovalQueue, HITLManager
+
+__all__ = ["ApprovalQueue", "HITLManager"]