Generate a FastAPI project with SQLAlchemy and SQLite. Follow the REFERENCE IMPLEMENTATION exactly.

Generate these 4 files with === markers:

=== models.py ===
=== schemas.py ===
=== main.py ===
=== test_main.py ===

Key patterns (copy from reference):
- class Base(DeclarativeBase): pass
- Mapped[str] = mapped_column(String(255))
- Mapped[str | None] = mapped_column(Text, default=None)
- model_config = ConfigDict(from_attributes=True)
- model_dump() not dict()
- POST 201, GET list, GET by id 404, PUT, DELETE 204

CRITICAL:
- Use ONLY fields from the JSON spec — no created_at or extra fields
- Generate EXACTLY 6 tests per entity: create, list, get_by_id, not_found, update, delete
- No search, filter, or other extra tests
- No markdown fences in output