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

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

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

@@ -1 +1,23 @@
-"""${dir} module."""
+"""Emergency controls for agent safety."""
+
+from .controls import (
+    EmergencyControls,
+    EmergencyEvent,
+    EmergencyReason,
+    EmergencyState,
+    EmergencyTrigger,
+    check_emergency_allowed,
+    emergency_stop_global,
+    get_emergency_controls,
+)
+
+__all__ = [
+    "EmergencyControls",
+    "EmergencyEvent",
+    "EmergencyReason",
+    "EmergencyState",
+    "EmergencyTrigger",
+    "check_emergency_allowed",
+    "emergency_stop_global",
+    "get_emergency_controls",
+]