- Add database indexes for admin queries (role, isActive+role, createdAt, lastLoginAt)
- Update setUserActive to track disabledAt and disabledBy fields
- Add getPaginatedUsers function with search, filter, sort support
- Add updateUserRole function for promoting/demoting users
- Create admin routes with full user management API:
- GET /api/admin/users - paginated list with search/filter/sort
- GET /api/admin/users/:id - user details with recent activity
- PATCH /api/admin/users/:id - enable/disable users
- PATCH /api/admin/users/:id/role - promote/demote users
- Add validation for ObjectId format and self-modification prevention
- All 53 Phase 1 backend tests passing
