fix(account): 同步上游模型失败时显示后端返回的错误原因

- apiClient 拒绝的是普通对象而非 Error，原写法 instanceof Error 恒为假，
  错误提示被替换成通用文案"同步上游模型失败：同步上游模型失败"
- 白名单选择器与 Antigravity 同步按钮改用 extractApiErrorMessage 取消息

frontend/src/components/account/EditAccountModal.vue

@@ -4771,7 +4771,7 @@ const syncAntigravityUpstreamModels = async () => {
       appStore.showWarning(t('admin.accounts.syncUpstreamModelsMetadataPartial'))
     }
   } catch (error) {
-    const message = error instanceof Error ? error.message : t('admin.accounts.syncUpstreamModelsFailed')
+    const message = extractApiErrorMessage(error, t('admin.accounts.syncUpstreamModelsFailed'))
     appStore.showError(t('admin.accounts.syncUpstreamModelsError', { message }))
   } finally {
     isSyncingAntigravityUpstream.value = false

frontend/src/components/account/ModelWhitelistSelector.vue

@@ -155,6 +155,7 @@ import ModelIcon from '@/components/common/ModelIcon.vue'
 import Icon from '@/components/icons/Icon.vue'
 import { allModels, getModelsByPlatform } from '@/composables/useModelWhitelist'
 import { supportsUpstreamModelSync } from '@/constants/platformCatalog'
+import { extractApiErrorMessage } from '@/utils/apiError'
 
 const { t } = useI18n()
 
@@ -343,7 +344,7 @@ const syncUpstreamModels = async () => {
       appStore.showWarning(t('admin.accounts.syncUpstreamModelsMetadataPartial'))
     }
   } catch (error) {
-    const message = error instanceof Error ? error.message : t('admin.accounts.syncUpstreamModelsFailed')
+    const message = extractApiErrorMessage(error, t('admin.accounts.syncUpstreamModelsFailed'))
     appStore.showError(t('admin.accounts.syncUpstreamModelsError', { message }))
   } finally {
     isSyncingUpstream.value = false

frontend/src/components/account/__tests__/ModelWhitelistSelector.spec.ts

@@ -29,7 +29,7 @@ vi.mock('vue-i18n', async () => {
   return {
     ...actual,
     useI18n: () => ({
-      t: (key: string, params?: Record<string, string>) => key === 'common.copy' ? '复制' : key === 'admin.accounts.modelMappingConflict' ? `Model mapping conflict: ${params?.from} → ${params?.to}` : key
+      t: (key: string, params?: Record<string, string>) => key === 'common.copy' ? '复制' : key === 'admin.accounts.modelMappingConflict' ? `Model mapping conflict: ${params?.from} → ${params?.to}` : key === 'admin.accounts.syncUpstreamModelsError' ? `${key}: ${params?.message}` : key
     })
   }
 })
@@ -244,6 +244,26 @@ describe('ModelWhitelistSelector', () => {
     expect(showSuccess).not.toHaveBeenCalled()
   })
 
+  it('shows the backend message when upstream sync is rejected', async () => {
+    syncUpstreamModels.mockRejectedValue({
+      status: 400,
+      code: 'BAD_REQUEST',
+      message: 'Vertex API key accounts do not support upstream model listing'
+    })
+    const wrapper = mountSelector({ platform: 'gemini', accountId: 174 })
+
+    const syncButton = wrapper
+      .findAll('button')
+      .find(button => button.text() === 'admin.accounts.syncUpstreamModels')
+    expect(syncButton).toBeDefined()
+    await syncButton!.trigger('click')
+    await flushPromises()
+
+    expect(showError).toHaveBeenCalledWith(
+      'admin.accounts.syncUpstreamModelsError: Vertex API key accounts do not support upstream model listing'
+    )
+  })
+
   it('shows success and a partial warning when some capabilities were saved', async () => {
     syncUpstreamModels.mockResolvedValue({
       models: ['gpt-6-astra', 'gpt-image-2'],