feat: 添加推送通知功能，支持Web Push订阅和发送

public/sw.js

@@ -21,3 +21,25 @@ self.addEventListener("fetch", (event) => {
   // If needed in future, add logic here, but keep it disabled for now.
   return;
 });
+
+self.addEventListener('push', function(event) {
+  if (event.data) {
+    const payload = event.data.json();
+    const title = payload.title || 'New Notification';
+    const options = {
+      body: payload.body,
+      icon: payload.icon || '/favicon.png',
+      badge: payload.badge || '/favicon.png',
+      data: payload.url || '/'
+    };
+
+    event.waitUntil(self.registration.showNotification(title, options));
+  }
+});
+
+self.addEventListener('notificationclick', function(event) {
+  event.notification.close();
+  event.waitUntil(
+    clients.openWindow(event.notification.data)
+  );
+});