fix(admin): 修复表格批量操作和搜索功能问题

1. 恢复账号管理批量操作栏缺失的功能按钮
   - 添加"本页全选"按钮支持批量选择当前页所有账号
   - 添加"清除已选"按钮快速清空已选账号列表
   - 在重构拆分组件时遗漏，现已恢复

2. 修复分组管理搜索功能仅搜索当前页的问题
   - 前端：移除本地过滤逻辑，改用后端搜索
   - 后端：添加 search 参数支持，搜索名称和描述字段
   - 支持不区分大小写的模糊匹配
   - 统一所有管理页面的搜索体验

frontend/src/views/admin/GroupsView.vue

@@ -16,6 +16,7 @@
                 type="text"
                 :placeholder="t('admin.groups.searchGroups')"
                 class="input pl-10"
+                @input="handleSearch"
               />
             </div>
           <Select
@@ -64,7 +65,7 @@
       </template>
 
       <template #table>
-        <DataTable :columns="columns" :data="displayedGroups" :loading="loading">
+        <DataTable :columns="columns" :data="groups" :loading="loading">
           <template #cell-name="{ value }">
             <span class="font-medium text-gray-900 dark:text-white">{{ value }}</span>
           </template>
@@ -932,16 +933,6 @@ const pagination = reactive({
 
 let abortController: AbortController | null = null
 
-const displayedGroups = computed(() => {
-  const q = searchQuery.value.trim().toLowerCase()
-  if (!q) return groups.value
-  return groups.value.filter((group) => {
-    const name = group.name?.toLowerCase?.() ?? ''
-    const description = group.description?.toLowerCase?.() ?? ''
-    return name.includes(q) || description.includes(q)
-  })
-})
-
 const showCreateModal = ref(false)
 const showEditModal = ref(false)
 const showDeleteDialog = ref(false)
@@ -1011,7 +1002,8 @@ const loadGroups = async () => {
     const response = await adminAPI.groups.list(pagination.page, pagination.page_size, {
       platform: (filters.platform as GroupPlatform) || undefined,
       status: filters.status as any,
-      is_exclusive: filters.is_exclusive ? filters.is_exclusive === 'true' : undefined
+      is_exclusive: filters.is_exclusive ? filters.is_exclusive === 'true' : undefined,
+      search: searchQuery.value.trim() || undefined
     }, { signal })
     if (signal.aborted) return
     groups.value = response.items
@@ -1030,6 +1022,15 @@ const loadGroups = async () => {
   }
 }
 
+let searchTimeout: ReturnType<typeof setTimeout>
+const handleSearch = () => {
+  clearTimeout(searchTimeout)
+  searchTimeout = setTimeout(() => {
+    pagination.page = 1
+    loadGroups()
+  }, 300)
+}
+
 const handlePageChange = (page: number) => {
   pagination.page = page
   loadGroups()