refactor(pwa): migrate from @ducanh2912/next-pwa to @serwist/turbopack

Next.js 16 ships Turbopack as the default bundler, but
@ducanh2912/next-pwa is webpack-only — the previous PWA setup
required `--webpack` on dev/build/"dev:proxy" scripts, accepting
a perf regression in exchange for working PWA install.

@serwist/turbopack (paired with the official 'serwist' package
and 'esbuild') is the Turbopack-native successor: it works with
the default bundler, no opt-out flag, and gives us a real TS
service worker source file we can read and edit.

What this commit does:

1. Swap deps in package.json:
   - Remove @ducanh2912/next-pwa
   - Add @serwist/turbopack, serwist, esbuild (all devDeps)
   - Drop --webpack flag from dev / dev:proxy / build scripts
     (Turbopack is restored as the bundler)

2. next.config.ts:
   - Replace withPWAInit wrapping with withSerwist named import
   - Update comment block to describe new architecture

3. New src/app/sw.ts: Serwist service worker source.
   skipWaiting + clientsClaim + navigationPreload + defaultCache.
   This file is compiled to a real SW at build time by Serwist.

4. New src/app/serwist/[[...slug]]/route.ts: catch-all Route
   Handler that serves the compiled SW at /serwist/sw.js plus
   Serwist's chunked runtime assets. Catch-all is required
   because Serwist serves multiple files under /serwist/.

5. src/app/layout.tsx: replace <SwRegister /> with
   <SerwistProvider swUrl="/serwist/sw.js"> from
   @serwist/turbopack/react. The provider handles registration
   + lifecycle internally.

6. Delete src/app/_components/core/sw-register.tsx: replaced
   by SerwistProvider.

7. .gitignore: add public/sw.js and public/workbox-*.js
   (defensive — these are build artifacts that change hash
   every build and shouldn't be committed).

8. Untrack public/workbox-3c9d0171.js: stale workbox runtime
   from the previous next-pwa build, hash is build-specific
   so it can never be regenerated correctly.

Not modified (intentionally):
- src/utils/pwa.ts: pure beforeinstallprompt browser-API wrapper,
  library-agnostic, stays as-is.
- pwa-install-overlay / pwa-install-dialog: install UI flow
  unchanged.
- public/manifest.json: still works; layout's metadata.manifest
  points at it.

Verification:
- pnpm install resolved cleanly (added 24 pkgs, removed 209)
- npx tsc --noEmit passes (EXIT=0)
- Serwist provides named exports, not default — withSerwist and
  createSerwistRoute are both named imports

src/app/layout.tsx

@@ -1,9 +1,9 @@
 import type { Metadata, Viewport } from "next";
+import { SerwistProvider } from "@serwist/turbopack/react";
 import { SessionProvider } from "@/providers/session-provider";
 import { geistSans, geistMono, athelas } from "@/core/fonts";
 import "./globals.css";
 
-import { SwRegister } from "@/app/_components/core/sw-register";
 import { RootProviders } from "@/providers/root-providers";
 
 export const metadata: Metadata = {
@@ -51,9 +51,9 @@ export default function RootLayout({
         {/* NextAuth SessionProvider：为所有客户端组件提供 useSession() 上下文 */}
         <SessionProvider>
           <RootProviders>
-            {children}
-            {/* PWA Service Worker 注册器 —— 生产构建挂载 /sw.js（@ducanh2912/next-pwa 生成） */}
-            <SwRegister />
+            {/* PWA Service Worker 注册器 —— Serwist Turbopack 在 build 时编译 app/sw.ts，
+                通过 /serwist/sw.js 路由 handler 服务。SerwistProvider 内部处理注册 + 生命周期。 */}
+            <SerwistProvider swUrl="/serwist/sw.js">{children}</SerwistProvider>
           </RootProviders>
         </SessionProvider>
       </body>