feat: implement Admin Dashboard and Analytics API

[Ryjen1]

I have finished the Admin Dashboard and Analytics API.

Here is a breakdown of what is in this PR:

• Admin Module: Set up the core admin structure with audit logging to track all administrative actions.
• Management Endpoints: Added full CRUD for puzzles, user management (roles/status), and moderation queues for user submissions.
• Analytics & Health: New controllers for platform metrics and real-time system health monitoring.
• Security: Secured everything with RBAC and fixed a bug in RolesGuard that was breaking dependency injection.
• Tests: Added unit tests for the new admin controllers to make sure everything works as expected.

Everything is verified and ready for review.

Closes #149

[Mkalbani]

@Ryjen1 Please resolve conflict

[Ryjen1]

@Mkalbani Resolved!