feat: Enhance API documentation and response schemas for GitHub auth, global settings, and roles

- Added detailed OpenAPI documentation for GitHub OAuth login and callback routes, including response schemas for success and error cases.
- Introduced comprehensive response schemas for global settings API, including health checks, bulk operations, and category retrieval.
- Improved roles API with structured response schemas for role management, including permissions retrieval and error handling.
- Updated root health check endpoint to return additional service information, including timestamp and version.

Author: Lasim