feat: 网盘设置加「默认账号」列, 同类型最多2个主账号

- 数据库 migration: cloud_configs 加 is_primary 字段
- 后端: togglePrimary API (PUT /admin/cloud-configs/:id/primary)
- 后端: getAndValidateCredential 优先选 is_primary 账号
- 前端: CloudConfig.vue 转存启用后加「默认账号」开关列
- 前端: api/index.ts 加 setPrimary 方法

packages/frontend/src/api/index.ts

@@ -267,6 +267,14 @@ export async function deleteCloudConfig(
   await api.delete(`/admin/cloud-configs/${id}`)
 }
 
+export async function setPrimary(
+  id: number,
+  primary: boolean
+): Promise<any> {
+  const { data } = await api.put(`/admin/cloud-configs/${id}/primary`, { primary })
+  return data
+}
+
 export async function getStats(days?: number): Promise<StatsData> {
   const params: Record<string, number> = {}
   if (days) params.days = days

packages/frontend/src/pages/admin/CloudConfig.vue

@@ -99,6 +99,16 @@
           />
         </template>
       </el-table-column>
+      <el-table-column label="默认账号" width="100" align="center">
+        <template #default="{ row }">
+          <el-switch
+            :model-value="row.is_primary === 1"
+            :disabled="!row.is_transfer_enabled"
+            size="small"
+            @change="(val: boolean) => handleTogglePrimary(row, val)"
+          />
+        </template>
+      </el-table-column>
       <el-table-column label="操作" width="390" align="center">
         <template #default="{ row }">
           <el-button text type="primary" @click="openDialog(row)">编辑</el-button>
@@ -171,7 +181,7 @@ import { Loading } from '@element-plus/icons-vue'
 import { CLOUD_LABELS } from '../../types'
 import type { CloudType, CloudConfig } from '../../types'
 import { ElMessage } from 'element-plus'
-import { getCloudConfigs, saveCloudConfig, updateCloudConfig, deleteCloudConfig, testCloudConnection, getCloudTypes, toggleCloudType } from '../../api'
+import { getCloudConfigs, saveCloudConfig, updateCloudConfig, deleteCloudConfig, testCloudConnection, getCloudTypes, toggleCloudType, setPrimary } from '../../api'
 import CloudBadge from '../../components/CloudBadge.vue'
 import type { ElForm } from 'element-plus'
 
@@ -351,6 +361,16 @@ async function handleToggleTransfer(row: CloudConfig, enabled: boolean) {
   }
 }
 
+async function handleTogglePrimary(row: CloudConfig, enabled: boolean) {
+  try {
+    await setPrimary(row.id!, enabled)
+    row.is_primary = enabled ? 1 : 0
+    ElMessage.success(enabled ? `已将「${row.nickname || row.cloud_type}」设为默认账号` : '已取消默认账号')
+  } catch (e: any) {
+    ElMessage.error(e.response?.data?.error || e.message || '操作失败')
+  }
+}
+
 async function autoVerifyAll() {
   for (const cfg of configs.value) {
     if (cfg.cookie_preview || cfg.nickname) {