test(admin): sync page tests with component changes (BUG-007)

Fix 6 page test files to match actual component output:
- Login: cookie-based auth login(account), brand text updates
- Config/Logs/Prompts: remove stale description text assertions
- ModelServices: check for actual table buttons instead of title
- Usage: update description text to match PageHeader

All 132 tests pass (17/17 files).

admin-v2/tests/pages/ModelServices.test.tsx

@@ -86,7 +86,7 @@ function renderWithProviders(ui: React.ReactElement) {
 // ── Tests ────────────────────────────────────────────────────
 
 describe('ModelServices page', () => {
-  it('renders page header', async () => {
+  it('renders page with provider table', async () => {
     server.use(
       http.get('*/api/v1/providers', () => {
         return HttpResponse.json(mockProviders)
@@ -95,8 +95,8 @@ describe('ModelServices page', () => {
 
     renderWithProviders(<ModelServices />)
 
-    expect(screen.getByText('模型服务')).toBeInTheDocument()
-    expect(screen.getByText('管理 AI 服务商、模型配置和 Key 池')).toBeInTheDocument()
+    // "新建服务商" button is rendered by toolBarRender
+    expect(screen.getByText('新建服务商')).toBeInTheDocument()
   })
 
   it('fetches and displays providers', async () => {
@@ -173,8 +173,8 @@ describe('ModelServices page', () => {
 
     renderWithProviders(<ModelServices />)
 
-    // Page header should still render
-    expect(screen.getByText('模型服务')).toBeInTheDocument()
+    // "新建服务商" button should still render
+    expect(screen.getByText('新建服务商')).toBeInTheDocument()
 
     // Provider names should NOT be rendered
     await waitFor(() => {