feat: add notifications for MacOS using Applescript (#160)

yolo'ed it with codex. Let me know if this looks good to you.

https://github.com/openai/codex/issues/148

tested with:
```
npm run build:dev
```

<img width="377" alt="Screenshot 2025-04-16 at 18 12 01"
src="https://github.com/user-attachments/assets/79aa799b-b0b9-479d-84f1-bfb83d34bfb9"
/>

codex-cli/tests/agent-interrupt-continue.test.ts

@@ -41,6 +41,7 @@ describe("Agent interrupt and continue", () => {
       config: {
         model: "test-model",
         instructions: "",
+        notify: false,
       },
       onItem: (item) => received.push(item),
       onLoading: (loading) => {