fix: 用户管理筛选去掉管理员加企业用户，管理员不可换角色和删除

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/UserManagement.vue

@@ -91,10 +91,10 @@
         </div>
         <div class="user-actions">
           <select
+            v-if="u.role !== 'admin'"
             :value="u.role"
             class="role-select"
             @change="changeRole(u, $event.target.value)"
-            :disabled="u.role === 'admin'"
           >
             <option value="viewer">查看者</option>
             <option value="editor">编辑</option>
@@ -102,7 +102,7 @@
           </select>
           <button v-if="u.business_verified" class="btn-sm btn-outline" @click="revokeBusiness(u)" title="撤销商业认证">💼</button>
           <button v-else class="btn-sm btn-outline" @click="grantBusiness(u)" title="开通商业认证" style="opacity:0.3">💼</button>
-          <button class="btn-sm btn-delete" @click="removeUser(u)" title="删除用户">🗑️</button>
+          <button class="btn-sm btn-delete" @click="removeUser(u)" :disabled="u.role === 'admin'" title="删除用户">🗑️</button>
         </div>
       </div>
       <div v-if="filteredUsers.length === 0" class="empty-hint">未找到用户</div>
@@ -162,10 +162,10 @@ function formatDate(d) {
 }
 
 const roles = [
-  { value: 'admin', label: '管理员' },
   { value: 'senior_editor', label: '高级编辑' },
   { value: 'editor', label: '编辑' },
   { value: 'viewer', label: '查看者' },
+  { value: 'business', label: '企业用户' },
 ]
 
 const filteredUsers = computed(() => {
@@ -178,8 +178,12 @@ const filteredUsers = computed(() => {
     )
   }
   if (filterRole.value) {
+    if (filterRole.value === 'business') {
+      list = list.filter(u => u.business_verified)
+    } else {
       list = list.filter(u => u.role === filterRole.value)
     }
+  }
   return list
 })