### GA Engine Optimizations
- Changed `ensure_unique_items()` from O(n²) to O(n) using set
- Increased parent selection from top 10 to top 20 for better diversity
- Used `dict.fromkeys()` for faster stat initialization
### Type Safety
- Updated all type hints to Python 3.9+ style (list[dict] instead of List[Dict])
- Fixed type annotations in ga_engine.py, evaluator.py, passive_manager.py
### Test Coverage
- All 104 tests passing ✅
- Added comprehensive unit tests for GA engine, evaluator, and passive manager
### Files Changed
- app/core/ga_engine.py
- app/core/evaluator.py
- app/core/passive_manager.py
- tests/ (new test files)
