🔧 refactor: Integrate PrincipalModel Enum for Principal Handling

- Replaced string literals for principal models ('User', 'Group') with the new PrincipalModel enum across various models, services, and tests to enhance type safety and consistency.
- Updated permission handling in multiple files to utilize the PrincipalModel enum, improving maintainability and reducing potential errors.
- Ensured all relevant tests reflect these changes to maintain coverage and functionality.

api/models/PromptGroupMigration.spec.js

@@ -7,6 +7,7 @@ const {
   ResourceType,
   AccessRoleIds,
   PrincipalType,
+  PrincipalModel,
   PermissionBits,
 } = require('librechat-data-provider');
 
@@ -211,7 +212,7 @@ describe('PromptGroup Migration Script', () => {
     await AclEntry.create({
       principalType: PrincipalType.USER,
       principalId: testOwner._id,
-      principalModel: 'User',
+      principalModel: PrincipalModel.USER,
       resourceType: ResourceType.PROMPTGROUP,
       resourceId: promptGroup1._id,
       permBits: ownerRole.permBits,