Add emoji confetti bursts and component playground.

Support app.relay.emoji_confetti on jumbo emoji clicks with canvas physics,
per-emoji particle profiles, and a fixed overlay that does not affect scroll.
Also add a Vite playground for live component previews and theme hover preview.

src/playground/monacoSetup.ts

@@ -0,0 +1,12 @@
+import editorWorker from 'monaco-editor/esm/vs/editor/editor.worker?worker';
+import jsonWorker from 'monaco-editor/esm/vs/language/json/json.worker?worker';
+import tsWorker from 'monaco-editor/esm/vs/language/typescript/ts.worker?worker';
+
+// Vite-friendly Monaco workers (no AMD CDN loader).
+self.MonacoEnvironment = {
+  getWorker(_workerId: string, label: string) {
+    if (label === 'json') return new jsonWorker();
+    if (label === 'typescript' || label === 'javascript') return new tsWorker();
+    return new editorWorker();
+  },
+};