Fix PWA installation support

app/pwa-register.tsx

@@ -1,3 +1,23 @@
 "use client";
-import { useEffect } from "react";
-export default function PwaRegister() { useEffect(() => { if ("serviceWorker" in navigator) navigator.serviceWorker.register("/sw.js").catch(() => undefined); }, []); return null; }
+import { useEffect, useState } from "react";
+
+type InstallPrompt = Event & { prompt: () => Promise<void>; userChoice: Promise<{ outcome: "accepted" | "dismissed" }> };
+
+export default function PwaRegister() {
+  const [prompt, setPrompt] = useState<InstallPrompt | null>(null);
+  const [isIos, setIsIos] = useState(false);
+
+  useEffect(() => {
+    if ("serviceWorker" in navigator) navigator.serviceWorker.register("/sw.js", { updateViaCache: "none" }).catch(() => undefined);
+    setIsIos(/iphone|ipad|ipod/i.test(navigator.userAgent));
+    const receivePrompt = (event: Event) => { event.preventDefault(); setPrompt(event as InstallPrompt); };
+    window.addEventListener("beforeinstallprompt", receivePrompt);
+    return () => window.removeEventListener("beforeinstallprompt", receivePrompt);
+  }, []);
+
+  if (!prompt && !isIos) return null;
+  return <div className="pwa-install" role="status">
+    <span>把打卡站点安装到桌面，打开更快捷。</span>
+    {prompt ? <button onClick={async () => { await prompt.prompt(); const result = await prompt.userChoice; if (result.outcome === "accepted") setPrompt(null); }}>安装应用</button> : <span className="pwa-ios">Safari 点“分享”→“添加到主屏幕”</span>}
+  </div>;
+}