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/config.test.tsx

@@ -68,6 +68,7 @@ test("saves and loads config correctly", () => {
   const testConfig = {
     model: "test-model",
     instructions: "test instructions",
+    notify: false,
   };
   saveConfig(testConfig, testConfigPath, testInstructionsPath);