feat: OAuth 重复账号失效时允许覆盖更新，优化前端分页与刷新体验

- OAuth 去重逻辑改为：已失效的重复账号自动覆盖更新而非拒绝，
  适用于单个导入、批量导入、Kiro 导入等所有入口
- 新增 _update_existing_oauth_key 函数统一处理覆盖更新逻辑
- useSmartPagination 新增 fixedHeight 属性防止翻页时容器高度跳动
- ProviderDetailDrawer OAuth 刷新后仅重载 keys 数据避免整表刷新

frontend/src/composables/useSmartPagination.ts

@@ -39,6 +39,12 @@ export function useSmartPagination<T>(
     return Math.ceil(items.value.length / itemsPerPage.value)
   })
 
+  /** 分页激活时的固定高度（px），用于防止翻页时容器高度跳动 */
+  const fixedHeight = computed(() => {
+    if (!shouldPaginate.value || cachedAvgItemHeight.value <= 0) return undefined
+    return itemsPerPage.value * cachedAvgItemHeight.value
+  })
+
   /** 将当前页内的局部索引转换为全局索引 */
   function getGlobalIndex(localIdx: number): number {
     if (!shouldPaginate.value) return localIdx
@@ -165,6 +171,7 @@ export function useSmartPagination<T>(
     totalPages,
     shouldPaginate,
     paginatedItems,
+    fixedHeight,
     getGlobalIndex,
     detect,
     reset,

frontend/src/features/providers/components/ProviderDetailDrawer.vue

@@ -208,6 +208,7 @@
                   v-if="allKeys.length > 0"
                   ref="keysListRef"
                   class="divide-y divide-border/40"
+                  :style="keysFixedHeight ? { minHeight: keysFixedHeight + 'px' } : undefined"
                 >
                   <div
                     v-for="({ key, endpoint }, localIdx) in paginatedKeys"
@@ -1227,6 +1228,7 @@ const {
   totalPages: totalKeyPages,
   shouldPaginate: shouldPaginateKeys,
   paginatedItems: paginatedKeys,
+  fixedHeight: keysFixedHeight,
   getGlobalIndex: getGlobalKeyIndex,
   reset: resetKeysPagination,
 } = useSmartPagination(allKeys, keysListRef)
@@ -1494,8 +1496,13 @@ async function handleRefreshOAuth(key: EndpointAPIKey) {
     if (keyInList) {
       keyInList.oauth_expires_at = result.expires_at
     }
-    // 重新加载 key 数据（token 刷新可能补上了 project_id 等信息）
-    await loadEndpoints()
+    // 只重新加载 keys 数据，避免整个表格刷新
+    if (props.providerId) {
+      const freshKeys = await getProviderKeys(props.providerId).catch(() => null)
+      if (freshKeys) {
+        providerKeys.value = freshKeys
+      }
+    }
     // Antigravity：token 刷新后可能完成了账号激活，触发配额获取
     // （不 emit('refresh')，避免触发全局 provider 余额刷新）
     void autoRefreshQuotaInBackground()