feat: 添加推送通知功能，支持Web Push订阅和发送

app/api/push/vapid-public-key/route.ts

@@ -0,0 +1,9 @@
+import { NextResponse } from 'next/server';
+
+export async function GET() {
+  const publicKey = process.env.NEXT_PUBLIC_VAPID_PUBLIC_KEY;
+  if (!publicKey) {
+    return NextResponse.json({ error: 'VAPID public key not found' }, { status: 500 });
+  }
+  return NextResponse.json({ publicKey });
+}