refactor(db): streamline model imports and remove unused model exports

- Removed the export of models from the database connection module to simplify the structure.
- Updated various files to import models directly from the new centralized models module.
- Ensured consistency across the codebase by replacing mongoose model references with the new import paths.

api/server/routes/messages.js

@@ -16,7 +16,7 @@ const { cleanUpPrimaryKeyValue } = require('~/lib/utils/misc');
 const { getConvosQueried } = require('~/models/Conversation');
 const { countTokens } = require('~/server/utils');
 
-const Message = mongoose.models.Message;
+const Message = require('~/db/models').Message;
 
 const router = express.Router();
 router.use(requireJwtAuth);