feat: 用户等级改为下拉选择 + 禁止修改管理员/提升为管理员

- Users.vue: ElMessageBox.prompt → el-dialog + el-select 下拉
- Users.vue: 管理员行隐藏设置按钮，显示标签文本
- AdminController: 拒绝修改 MANAGER 账户等级，拒绝提升为 ADMIN
- 信任等级显示改为中文标签

web/src/views/Users.vue

@@ -9,7 +9,7 @@
         <el-table-column prop="trustLevel" label="信任等级" width="100">
           <template #default="scope">
             <el-tag :type="trustLevelType(scope.row.trustLevel)">
-              {{ scope.row.trustLevel }}
+              {{ trustLevelLabel(scope.row.trustLevel) }}
             </el-tag>
           </template>
         </el-table-column>
@@ -21,13 +21,37 @@
           </template>
         </el-table-column>
         <el-table-column prop="createdAt" label="注册时间" width="180" />
-        <el-table-column label="操作" width="150">
+        <el-table-column label="操作" width="120">
           <template #default="scope">
-            <el-button size="small" @click="handleSetLevel(scope.row)">设置等级</el-button>
+            <el-button
+              v-if="scope.row.trustLevel !== 'ADMIN'"
+              size="small"
+              @click="handleSetLevel(scope.row)"
+            >设置等级</el-button>
+            <span v-else style="color:#999;font-size:12px">管理员</span>
           </template>
         </el-table-column>
       </el-table>
     </el-card>
+
+    <!-- 等级设置弹窗 -->
+    <el-dialog v-model="dialogVisible" title="设置信任等级" width="400px">
+      <el-form :model="levelForm">
+        <el-form-item label="用户">
+          <span>{{ levelForm.email }}</span>
+        </el-form-item>
+        <el-form-item label="信任等级">
+          <el-select v-model="levelForm.level" placeholder="请选择等级" style="width: 100%">
+            <el-option label="普通成员 (MEMBER)" value="MEMBER" />
+            <el-option label="受信任 (TRUSTED)" value="TRUSTED" />
+          </el-select>
+        </el-form-item>
+      </el-form>
+      <template #footer>
+        <el-button @click="dialogVisible = false">取消</el-button>
+        <el-button type="primary" @click="confirmSetLevel" :loading="saving">确认</el-button>
+      </template>
+    </el-dialog>
   </div>
 </template>
 
@@ -36,12 +60,20 @@ import api from '../api'
 
 const users = ref([])
 const loading = ref(false)
+const dialogVisible = ref(false)
+const saving = ref(false)
+const levelForm = reactive({ id: null, email: '', level: '' })
 
 const trustLevelType = (level) => {
   const map = { MEMBER: '', TRUSTED: 'warning', ADMIN: 'danger' }
   return map[level] || ''
 }
 
+const trustLevelLabel = (level) => {
+  const map = { MEMBER: '普通成员', TRUSTED: '受信任', ADMIN: '管理员' }
+  return map[level] || level
+}
+
 const fetchUsers = async () => {
   loading.value = true
   try {
@@ -54,19 +86,28 @@ const fetchUsers = async () => {
   }
 }
 
-const handleSetLevel = async (row) => {
+const handleSetLevel = (row) => {
+  levelForm.id = row.id
+  levelForm.email = row.email
+  levelForm.level = row.trustLevel === 'ADMIN' ? '' : row.trustLevel
+  dialogVisible.value = true
+}
+
+const confirmSetLevel = async () => {
+  if (!levelForm.level) {
+    ElMessage.warning('请选择等级')
+    return
+  }
+  saving.value = true
   try {
-    const { value: level } = await ElMessageBox.prompt('请输入信任等级 (MEMBER/TRUSTED/ADMIN)', '设置信任等级', {
-      inputValue: row.trustLevel,
-      confirmButtonText: '确认',
-      cancelButtonText: '取消',
-      inputValidator: (v) => ['MEMBER', 'TRUSTED', 'ADMIN'].includes(v) ? true : '无效等级'
-    })
-    await api.users.setTrustLevel(row.id, level)
+    await api.users.setTrustLevel(levelForm.id, levelForm.level)
     ElMessage.success('设置成功')
+    dialogVisible.value = false
     fetchUsers()
   } catch (e) {
-    if (e !== 'cancel') ElMessage.error(e.response?.data?.message || '操作失败')
+    ElMessage.error(e.response?.data?.message || '操作失败')
+  } finally {
+    saving.value = false
   }
 }