- Add new `relationships` parameter to `create_models()` function
- Generate bidirectional relationships with `back_populates` for foreign keys
- Support both `sqlalchemy` and `sqlalchemy_v2` model types:
  - For sqlalchemy: uses `relationship("Model", back_populates="attr")`
  - For sqlalchemy_v2: uses `Mapped[List["Model"]]` and `Mapped["Model"]` type hints
- Add `collect_relationships()` function to gather FK relationships from tables
- Handle both inline FK references and ALTER TABLE FK definitions
- Add functional and integration tests for both model types
- Update CHANGELOG with new feature documentation