feat：新增安卓 pwa 支持

public/sw.js

@@ -0,0 +1,18 @@
+// 最小 Service Worker，满足 Android Chrome「添加到主屏幕」的安装条件
+const CACHE_NAME = 'jigubao-v1';
+
+self.addEventListener('install', (event) => {
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(self.clients.claim());
+});
+
+self.addEventListener('fetch', (event) => {
+  event.respondWith(
+    fetch(event.request).catch(() => {
+      return new Response('', { status: 503, statusText: 'Service Unavailable' });
+    })
+  );
+});