feat(web): 增加单点登录分流与本地应急入口

开启统一认证后，正常登录入口直接跳转认证中心，并将本地账号入口收敛到 /login 应急页；未开启统一认证时继续保留工作台内原有登录方式。

影响范围仅限 Web 登录路由、认证入口展示和相关测试，不修改认证接口或 OpenAPI。风险主要在运行时身份状态判断，已通过 141 项前端测试、生产构建、无缓存类型检查及浏览器分支验证。

apps/web/src/App.tsx

@@ -131,6 +131,7 @@ import {
 } from './lib/oidc-browser-session';
 import {
   consumeOIDCCallbackError,
+  loginEntryAction,
   loadOIDCRuntimeConfiguration,
   startOIDCLogin,
   startOIDCLogout,
@@ -138,6 +139,7 @@ import {
 import { runTask, type RunTaskOptions } from './lib/run-task';
 import { AdminPage } from './pages/AdminPage';
 import { ApiDocsPage } from './pages/ApiDocsPage';
+import { EmergencyLoginPage } from './pages/EmergencyLoginPage';
 import { HomePage } from './pages/HomePage';
 import { ModelsPage } from './pages/ModelsPage';
 import { PlaygroundPage } from './pages/PlaygroundPage';
@@ -686,6 +688,10 @@ export function App() {
       const response = await request();
       persistAccessToken(response.accessToken);
       setToken(response.accessToken);
+      if (activePage === 'login') {
+        navigatePath(pathForWorkspaceSection('overview'));
+        return;
+      }
       await ensureRouteData(response.accessToken, true);
     } catch (err) {
       setState('error');
@@ -1308,9 +1314,25 @@ export function App() {
     });
   }
 
-  function showLogin() {
-    setAuthMode('login');
-    navigatePath(pathForWorkspaceSection('overview'));
+  async function showLogin() {
+    setState('loading');
+    setError('');
+    try {
+      const configuration = await loadOIDCRuntimeConfiguration(true);
+      const identityEnabled = configuration.enabled && configuration.oidcLogin;
+      setOIDCEnabled(identityEnabled);
+      if (loginEntryAction(identityEnabled) === 'oidc') {
+        setOIDCCallbackError(null);
+        await startOIDCLogin(configuration);
+        return;
+      }
+      setState('idle');
+      setAuthMode('login');
+      navigatePath(pathForWorkspaceSection('overview'));
+    } catch (err) {
+      setState('error');
+      setError(err instanceof Error ? err.message : '登录入口加载失败');
+    }
   }
 
   function currentRouteState(): AppRouteState {
@@ -1411,6 +1433,14 @@ export function App() {
         />
       )}
       {activePage === 'models' && <ModelsPage data={data} />}
+      {activePage === 'login' && (
+        <EmergencyLoginPage
+          loginForm={loginForm}
+          state={state}
+          onLoginChange={setLoginForm}
+          onSubmitLogin={submitLogin}
+        />
+      )}
       {activePage === 'workspace' && (
         isAuthenticated ? (
           <WorkspacePage