chore: remove svelte-preprocess (#7159)

web/svelte.config.js

@@ -1,9 +1,9 @@
 import adapter from '@sveltejs/adapter-static';
-import preprocess from 'svelte-preprocess';
+import { vitePreprocess } from '@sveltejs/vite-plugin-svelte';
 
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
-  preprocess: preprocess(),
+  preprocess: vitePreprocess(),
   onwarn: (warning, handler) => {
     if (warning.code.includes('a11y')) {
       return;