fix: add --webpack flag for Next.js 16 Turbopack compatibility

- serwist/next requires webpack, Next.js 16 defaults to Turbopack
- dev/build scripts now use --webpack flag
- Disable serwist in dev mode to avoid warnings

next.config.ts

@@ -4,6 +4,7 @@ import withSerwistInit from '@serwist/next'
 const withSerwist = withSerwistInit({
   swSrc: 'src/sw.ts',
   swDest: 'public/sw.js',
+  disable: process.env.NODE_ENV === 'development',
 })
 
 const nextConfig: NextConfig = {