bug: Ctrl+Z does not undo pasted prompts in Amazon Q VS Code

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

If you're using the same Windows setup as before:

### Expected behaviour

When I type a prompt manually in Amazon Q and press `Ctrl+Z`, the text is undone correctly.

I expect the same behavior when I copy and paste a prompt. Pressing `Ctrl+Z` should undo the pasted text.

### Actual behaviour

When I copy and paste a prompt into Amazon Q in VS Code and press `Ctrl+Z`, the pasted text is not undone.

Interestingly, `Ctrl+Z` works correctly when the prompt is typed manually.

This is a small issue, but it can be frustrating when working in a rush. It happens repeatedly and interrupts the workflow because I have to manually remove or correct the pasted prompt.

I have attached a video demonstrating the issue.

### Steps to reproduce

1. Open VS Code with Amazon Q Developer.
2. Open the Amazon Q chat/input area.
3. Type some text manually.
4. Press `Ctrl+Z` — the typed text is undone correctly.
5. Copy a prompt/text from another application.
6. Paste the prompt into Amazon Q.
7. Press `Ctrl+Z`.
8. Observe that the pasted prompt is not undone.

**Expected:** The pasted prompt should be removed/undone.

**Actual:** `Ctrl+Z` does not undo the pasted prompt.

### Environment

```yaml
OS: Windows 11
Editor: Visual Studio Code
Amazon Q: Amazon Q Developer VS Code extension
Amazon Q CLI: Not installed / `q` command is not recognized
```

First reproduce the issue in the Amazon Q chat/input area in VS Code using the listed Windows 11 steps, comparing manually typed and pasted text. Trace the VS Code input handling involved and verify that Ctrl+Z removes pasted prompts while preserving the existing manual-typing behavior.

Written by the indexing model from the issue text.