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-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/types/routes.d.ts";
+import "./.next/dev/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.