✨ STRIDE Category Validation:
- Add stride_validator.py with normalize_stride_category function
- Implement STRIDE validation in API endpoints (manual + AI threats)
- Add validation in CRUD operations for threat updates
- Ensure data consistency across all threat creation/update paths

🐛 API Cleanup:
- Remove duplicate imports in api.py
- Fix indentation issues
- Remove obsolete commented code
- Organize imports by category (stdlib, third-party, local)

🗂️ File Management Improvements:
- Implement UUID-based filenames for uploaded diagrams
- Add file extension validation for security
- Return both base64 and saved filename from save_image()
- Prevent filename collisions and security issues

🐳 Docker Persistence:
- Add diagrams_data volume for persistent diagram storage
- Configure nginx to serve diagrams directly from volume
- Fix diagram loss on container restart/rebuild
- Remove obsolete docker-compose version attribute

🎨 Frontend Enhancements:
- Implement compact STRIDE dropdown (shows first letter only)
- Add ResidualRiskSelector pattern for better UX
- Maintain consistent STRIDE categories between frontend/backend

🛡️ Security & Consistency:
- All STRIDE categories normalized to standard format
- Case-insensitive validation with fallback to 'Spoofing'
- File type validation prevents malicious uploads
- Centralized validation logic in stride_validator module