Move UI into its own page.

vite.config.ts

@@ -1,7 +1,16 @@
+import { resolve } from 'path'
 import { defineConfig } from 'vite'
 import preact from '@preact/preset-vite'
 
 // https://vitejs.dev/config/
 export default defineConfig({
-  plugins: [preact()]
+  plugins: [preact()],
+  build: {
+    rollupOptions: {
+      input: {
+        main: resolve(__dirname, 'index.html'),
+        ui: resolve(__dirname, 'ui/index.html')
+      }
+    }
+  }
 })