admin: add role management endpoints + Admin UI; strengthen RBAC and add tests

modern/frontend/src/AdminUsers.jsx

@@ -0,0 +1,28 @@
+import React, {useState, useEffect} from 'react'
+
+export default function AdminUsers(){
+  const [users, setUsers] = useState([])
+  const [msg, setMsg] = useState(null)
+
+  useEffect(()=>{
+    fetch('/api/v1/admin/users', {credentials:'include'}).then(r=>r.json()).then(setUsers).catch(()=>setUsers([]))
+  }, [])
+
+  function setRole(id, role){
+    fetch(`/api/v1/admin/users/${id}/role`, {method:'POST', credentials:'include', headers:{'Content-Type':'application/json'}, body: JSON.stringify({role})})
+      .then(r=>r.json()).then(()=> setMsg('Role updated'))
+      .catch(()=> setMsg('Failed'))
+  }
+
+  return (
+    <div style={{marginTop:20}}>
+      <h2>Admin: Users</h2>
+      {msg && <div style={{color:'#0366d6'}}>{msg}</div>}
+      <ul>
+        {users && users.length ? users.map(u=> (
+          <li key={u.id}>{u.email} — {u.role} <button onClick={()=>setRole(u.id,'moderator')} style={{marginLeft:8}}>Make Moderator</button> <button onClick={()=>setRole(u.id,'admin')} style={{marginLeft:8}}>Make Admin</button></li>
+        )): <li>No users</li>}
+      </ul>
+    </div>
+  )
+}

modern/frontend/src/App.jsx

@@ -2,6 +2,7 @@ import React from 'react'
 import Integrations from './Integrations'
 import Guilds from './Guilds'
 import Login from './Login'
+import AdminUsers from './AdminUsers'
 
 export default function App() {
     return (
@@ -11,6 +12,7 @@ export default function App() {
             <Login />
             <Integrations />
             <Guilds />
+            <AdminUsers />
         </div>
     )
 }