feat: add user role system and public joke submission API

- Add AdminUser role field (admin/submitter)
- User management in admin panel
- Public joke submission API (no auth required)
- Document submission methods for external workers

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

admin/src/api/user.js

@@ -0,0 +1,7 @@
+import request from './request'
+
+export const getUsers = () => request.get('/admin/users')
+
+export const createUser = (data) => request.post('/admin/users', data)
+
+export const deleteUser = (id) => request.delete(`/admin/users/${id}`)