Implement Admin User Management Endpoints

[ayshadogo]

Description:
Create admin endpoints for user management.

Tasks:

• Create GET /admin/users with pagination
• Add filters: role, kyc_status, created_date
• Create GET /admin/users/:id endpoint
• Create PATCH /admin/users/:id/role endpoint
• Create DELETE /admin/users/:id (soft delete)
• Protect all routes with admin role guard

Acceptance Criteria:

• Only admins can access endpoints
• Pagination works correctly
• Filters return accurate results
• Soft delete preserves data

---