feat(frontend): add routing skeleton with workspace chat and login pages

src/layouts/AppLayout.tsx

@@ -0,0 +1,19 @@
+import { Link, Outlet } from 'react-router-dom'
+
+export default function AppLayout() {
+  return (
+    <div style={{ display: 'grid', gridTemplateColumns: '220px 1fr', minHeight: '100vh' }}>
+      <aside style={{ borderRight: '1px solid #ddd', padding: 16 }}>
+        <h3>Fabric</h3>
+        <nav style={{ display: 'grid', gap: 8 }}>
+          <Link to="/workspace">工作台</Link>
+          <Link to="/chat">聊天</Link>
+          <Link to="/login">登录</Link>
+        </nav>
+      </aside>
+      <main style={{ padding: 16 }}>
+        <Outlet />
+      </main>
+    </div>
+  )
+}