Remove migration code and alembic dependency

src/server/api/auth.py

@@ -31,7 +31,6 @@ async def setup_auth(req: SetupRequest):
     
     This endpoint also initializes the configuration with default values
     and saves the anime directory and master password hash.
-    If anime_directory is provided, runs migration for existing data files.
     """
     if auth_service.is_configured():
         raise HTTPException(