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-cancel.test.ts

@@ -89,7 +89,7 @@ describe("Agent cancellation", () => {
     const agent = new AgentLoop({
       model: "any",
       instructions: "",
-      config: { model: "any", instructions: "" },
+      config: { model: "any", instructions: "", notify: false },
       approvalPolicy: { mode: "auto" } as any,
       additionalWritableRoots: [],
       onItem: (item) => {
@@ -140,7 +140,7 @@ describe("Agent cancellation", () => {
       additionalWritableRoots: [],
       model: "any",
       instructions: "",
-      config: { model: "any", instructions: "" },
+      config: { model: "any", instructions: "", notify: false },
       approvalPolicy: { mode: "auto" } as any,
       onItem: (item) => received.push(item),
       onLoading: () => {},