Switch from svite to vite + vite-plugin-svelte.

Use cross-env to set environment variables platform independently in scripts.

docs/vite.config.js

@@ -1,6 +1,10 @@
-module.exports = {
+import { defineConfig } from "vite";
+import { svelte } from "@sveltejs/vite-plugin-svelte";
+
+export default defineConfig({
+  plugins: [svelte()],
   optimizeDeps: {
     include: ["clipboard-copy", "flatpickr/dist/plugins/rangePlugin"],
     exclude: ["@sveltech/routify"],
   },
-};
+});