test: update test suite for SQLAlchemy 2.0 migration

- Add session fixture for async session management
- Update all test files to use session parameter
- Convert Core-style queries to ORM-style in tests
- Fix controller calls to include session parameter
- Remove obsolete get_database() references

Test progress: 108/195 tests passing

server/tests/conftest.py

@@ -84,6 +84,14 @@ async def setup_database(postgres_service):
         await async_engine.dispose()
 
 
+@pytest.fixture
+async def session():
+    from reflector.db import get_session_factory
+
+    async with get_session_factory()() as session:
+        yield session
+
+
 @pytest.fixture
 def dummy_processors():
     with (