Add admin protected routes for client management

The Admin UI will need new endpoints to meet some of the requirements. Below is a list of them that are ready to be implemented.

Notes:

If you choose to implement one, please create a new issue and add this as the parent issue. You also have free range to refactor or create new files if you believe it is necessary.

Documentation for the new endpoints would also need to be added.

Related files:

• middleware.go
• routes.go
• roles.go

Endpoints:

• GET /admin/clients — List all clients
• GET /admin/clients/:client_id — Get client details
• POST /admin/clients — Register a new client (static)
• PUT /admin/clients/:client_id — Update client details (full overwrite)
• PATCH /admin/clients/:client_id — Partial update (optional)
• DELETE /admin/clients/:client_id — Delete or deactivate clients
• GET /admin/audits - Get all audit events
• GET /admin/audits/clients/:client_id - Get all audit events for a specific client
• GET /admin/audits?type={event_type} - Get all audit events by type.