优化 GET /api/roles/users 用户列表的排序：
- 主排序：按角色等级 皇帝 → 公爵 → 骑士 → 平民（无角色用户排最后）
- 次排序：用户名长度（短者优先）
- 末排序：用户名字母序（大小写不敏感）
- 查询由 db.query.users.findMany（relational）改为显式 select + leftJoin，
以支持基于角色名的 CASE 排序
Sort the user list returned by GET /api/roles/users:
- Primary: by role rank Emperor -> Duke -> Knight -> Civilian (users
without a role sort last)
- Secondary: username length (shorter first)
- Tertiary: username alphabetical order (case-insensitive)
- Switch the query from db.query.users.findMany (relational) to an explicit
select + leftJoin to enable CASE-based ordering on role name
Redesign the Emperor's Role Management panel from a single-user
search-and-assign form into a full user management dashboard with
browsable user list and inline role editing.
stevenlee87