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

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -1 +1,5 @@
-"""${dir} module."""
+"""Rollback management for agent actions."""
+
+from .manager import RollbackManager, TransactionContext
+
+__all__ = ["RollbackManager", "TransactionContext"]