vercel: use official plaiceholder plugin

next.config.mjs

@@ -1,4 +1,7 @@
 // @ts-check
+
+import withPlaiceholder from "@plaiceholder/next";
+
 /**
  * Run `build` or `dev` with `SKIP_ENV_VALIDATION` to skip env validation.
  * This is especially useful for Docker builds.
@@ -58,4 +61,4 @@ const config = {
     ];
   },
 };
-export default config;
+export default withPlaiceholder(config);