🔐 Guardian Contract Security Enhancements:
- Add persistent SQLite storage for spending history and pending operations
- Replace in-memory state with database-backed state management
- Implement _init_storage(), _load_state(), _save_state() for state persistence
- Add _load_spending_history(), _save_spending_record() for transaction tracking
- Add _load_pending_operations(), _save_pending_operation(), _remove_pending_operation()
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