fix: 修复秒杀活动发布后状态未更新的问题

根因：publishFlashSale() 只做了缓存预热，从未调用 updateStatus()
将状态从1（未开始）更新为2（进行中），导致发布后UI无变化，
且活动无法被"进行中"查询找到。

修复内容：
- publishFlashSale() 添加 updateStatus(id, 2) 和缓存更新
- 简化 getFlashSaleList 状态查询，直接按 status 字段过滤
- 新增 findByStatus 仓库方法
- 前后端全面支持 PAUSED(status=4) 状态
- 修复管理后台"恢复"按钮错误显示在"已结束"状态上

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

flash-sale-frontend/src/pages/admin/flashsales.vue

@@ -43,6 +43,7 @@
       <el-select v-model="query.status" clearable placeholder="全部状态" @change="handleSearch">
         <el-option label="即将开始" value="UPCOMING" />
         <el-option label="进行中" value="ACTIVE" />
+        <el-option label="已暂停" value="PAUSED" />
         <el-option label="已结束" value="ENDED" />
       </el-select>
       <el-button type="primary" @click="handleSearch">搜索</el-button>
@@ -88,8 +89,8 @@
             <el-button text type="primary" @click="openEditDialog(row)">编辑</el-button>
             <el-button v-if="row.status === 'UPCOMING'" text type="success" @click="changeStatus('publish', row)">发布</el-button>
             <el-button v-if="row.status === 'ACTIVE'" text type="warning" @click="changeStatus('pause', row)">暂停</el-button>
-            <el-button v-if="row.status === 'ENDED'" text type="success" @click="changeStatus('resume', row)">恢复</el-button>
-            <el-button v-if="row.status !== 'ENDED'" text type="danger" @click="changeStatus('end', row)">结束</el-button>
+            <el-button v-if="row.status === 'PAUSED'" text type="success" @click="changeStatus('resume', row)">恢复</el-button>
+            <el-button v-if="row.status === 'ACTIVE' || row.status === 'PAUSED'" text type="danger" @click="changeStatus('end', row)">结束</el-button>
             <el-button text type="danger" @click="removeFlashSale(row)">删除</el-button>
           </template>
         </el-table-column>
@@ -253,6 +254,7 @@ const getStatusText = (status: string) => {
   const map: Record<string, string> = {
     UPCOMING: '即将开始',
     ACTIVE: '进行中',
+    PAUSED: '已暂停',
     ENDED: '已结束',
   }
   return map[status] || status
@@ -262,6 +264,7 @@ const getStatusType = (status: string) => {
   const map: Record<string, string> = {
     UPCOMING: 'warning',
     ACTIVE: 'danger',
+    PAUSED: 'warning',
     ENDED: 'info',
   }
   return map[status] || 'info'