Add prettier; Move svelte-preprocess from dependencies to devDependencies

src/frontend/vite.config.js

@@ -1,6 +1,6 @@
-import { sveltekit } from '@sveltejs/kit/vite';
-import { defineConfig } from 'vite';
+import { sveltekit } from "@sveltejs/kit/vite";
+import { defineConfig } from "vite";
 
 export default defineConfig({
-	plugins: [sveltekit()]
+  plugins: [sveltekit()],
 });