Fix async generator exception handling and add comprehensive tests

src/server/utils/dependencies.py

@@ -170,12 +170,7 @@ async def get_optional_database_session() -> AsyncGenerator:
         from src.server.database import get_db_session
         
         async with get_db_session() as session:
-            try:
-                yield session
-            except Exception:
-                # Re-raise the exception to let FastAPI handle it
-                # This prevents "generator didn't stop after athrow()" error
-                raise
+            yield session
     except (ImportError, RuntimeError):
         # Database not available - yield None
         yield None