Add installable PWA support

app/layout.tsx

@@ -1,5 +1,6 @@
 import type { Metadata } from "next";
 import "./globals.css";
+import PwaRegister from "./pwa-register";
 
 export const metadata: Metadata = {
   title: "大学英语六级 · 90天打卡",
@@ -8,6 +9,9 @@ export const metadata: Metadata = {
     icon: "/favicon.svg",
     shortcut: "/favicon.svg",
   },
+  manifest: "/manifest.webmanifest",
+  applicationName: "大学英语六级 · 90天打卡",
+  themeColor: "#1d4ed8",
 };
 
 export default function RootLayout({
@@ -17,7 +21,7 @@ export default function RootLayout({
 }>) {
   return (
     <html lang="zh-CN">
-      <body className="antialiased">{children}</body>
+      <body className="antialiased"><PwaRegister />{children}</body>
     </html>
   );
 }

app/pwa-register.tsx

@@ -0,0 +1,3 @@
+"use client";
+import { useEffect } from "react";
+export default function PwaRegister() { useEffect(() => { if ("serviceWorker" in navigator) navigator.serviceWorker.register("/sw.js").catch(() => undefined); }, []); return null; }

public/manifest.webmanifest

@@ -0,0 +1,12 @@
+{
+  "name": "大学英语六级 · 90天打卡",
+  "short_name": "CET-6 打卡",
+  "description": "CET-6 90 天复习计划、云端打卡与复盘。",
+  "lang": "zh-CN",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#eef4ff",
+  "theme_color": "#1d4ed8",
+  "icons": [{ "src": "/favicon.svg", "sizes": "any", "type": "image/svg+xml", "purpose": "any maskable" }]
+}