Refactor database initialization and remove Alembic migrations

- Removed legacy Alembic migration files and consolidated schema management into a new Pydantic-backed initializer (`scripts/init_db.py`).
- Updated `main.py` to ensure the new DB initializer runs on startup, maintaining idempotency.
- Adjusted session management in `config/database.py` to prevent DetachedInstanceError.
- Introduced new enums in `models/enums.py` for better organization and clarity.
- Refactored various models to utilize the new enums, improving code maintainability.
- Enhanced middleware to handle JSON validation more robustly, ensuring non-JSON requests do not trigger JSON errors.
- Added tests for middleware and enums to ensure expected behavior and consistency.
- Updated changelog to reflect significant changes and improvements.

config/database.py

@@ -54,7 +54,15 @@ def _build_database_url() -> str:
 DATABASE_URL = _build_database_url()
 
 engine = create_engine(DATABASE_URL, echo=True, future=True)
-SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+# Avoid expiring ORM objects on commit so that objects returned from UnitOfWork
+# remain usable for the duration of the request cycle without causing
+# DetachedInstanceError when accessed after the session commits.
+SessionLocal = sessionmaker(
+    autocommit=False,
+    autoflush=False,
+    bind=engine,
+    expire_on_commit=False,
+)
 Base = declarative_base()