🚀 Major Features Implemented:
- Automatic Mermaid ERD generation from SQLModel definitions
- Bidirectional relationship deduplication for clean diagrams
- Comprehensive validation system with syntax checking
- CLI interface for ERD generation and management
- Performance-optimized generation (<30 seconds for 20 tables)

📦 Package Migration:
- Moved all ERD code to dedicated backend/erd package
- Renamed files to remove erd_ prefix (now in erd package)
- Updated all imports across 17+ files
- Reorganized test structure under tests/unit/erd_tests/

🔧 Production Optimization:
- Updated .dockerignore to exclude ERD package from production builds
- Clean separation between core app and documentation tools
- ERD functionality can be excluded from production deployments

🧪 Testing & Quality:
- Comprehensive unit tests for all ERD components
- Performance tests ensuring <30 second generation time
- Integration tests for complete workflows
- Contract tests for CLI interface validation

📚 Documentation & Governance:
- Updated constitution with ERD requirements and performance standards
- Enhanced plan and tasks templates with ERD checks
- Complete ERD documentation with usage examples
- Generated sample ERD diagram (docs/database/erd.mmd)

✅ All Phase 3.5 tasks completed:
- T023-T025: Unit tests for ERD Generator, Model Metadata, validation
- T026: Performance tests (<30 seconds for large schemas)
- T027: Documentation updates
- T028: Constitution updates with ERD requirements
- T029-T030: Template updates with ERD checks
- T031: Code optimization and deduplication
- T032: Manual validation testing

The ERD system is now production-ready with clean architecture,
comprehensive testing, and optimized deployment configuration.