Add embeddable /embed widget and copy-paste snippet.

vite.config.ts

@@ -1,4 +1,5 @@
 import { defineConfig } from 'vite'
+import { resolve } from 'node:path'
 
 export default defineConfig({
   server: {
@@ -7,5 +8,11 @@ export default defineConfig({
   build: {
     outDir: 'dist',
     sourcemap: true,
+    rollupOptions: {
+      input: {
+        main: resolve(__dirname, 'index.html'),
+        embed: resolve(__dirname, 'embed.html'),
+      },
+    },
   },
 })