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/services/twoFactorService.js

@@ -2,7 +2,7 @@ const mongoose = require('mongoose');
 const { webcrypto } = require('node:crypto');
 const { hashBackupCode, decryptV3, decryptV2 } = require('~/server/utils/crypto');
 
-const User = mongoose.models.User;
+const User = require('~/db/models').User;
 
 // Base32 alphabet for TOTP secret encoding.
 const BASE32_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';