refactor(tts): replace Bun-specific APIs with execa and Node.js stdlib

- Replace `$` and `Bun.spawn` with `execa` for process execution
- Swap `Bun.JSONL.parse` for native `JSON.parse` and use `node:readline` for stdin handling

package.json

@@ -28,7 +28,8 @@
     "ai": "^6.0.161",
     "ansi-styles": "^6.2.3",
     "chalk": "^5.6.2",
-    "happy-dom-without-node": "^14.12.3",
+    "execa": "^9.6.1",
+    "happy-dom": "^20.10.2",
     "marked": "^18.0.4",
     "rolldown": "^1.0.3",
     "shiki": "^4.0.2",