✨ feat(mobile): add elderly university page

- create basic structure for ElderlyUniversityPage component
- add header with "老年大学" title
- include placeholder content indicating page is under development

src/client/mobile/pages/ElderlyUniversityPage.tsx

@@ -0,0 +1,16 @@
+import React from 'react';
+
+const ElderlyUniversityPage = () => {
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <header className="bg-blue-600 text-white p-4">
+        <h1 className="text-xl font-bold">老年大学</h1>
+      </header>
+      <div className="p-4">
+        <p className="text-center text-gray-500 py-8">老年大学页面开发中...</p>
+      </div>
+    </div>
+  );
+};
+
+export default ElderlyUniversityPage;