[AzureDevOpsExtension] Inline work item attachment images do not render in canvas

### Affected version or release

1.0.80

### Installation context

GitHub Copilot app on Windows, using the built-in Azure DevOps canvas to view a work item.

### What happened?

Images uploaded as Azure DevOps work item attachments and embedded inline in the work item description do not render in the Azure DevOps canvas. The canvas shows a broken-image icon followed by the image alt text. The rest of the description renders normally.

The same description, including its inline images, renders correctly in the Azure DevOps web UI.

### Steps to reproduce

1. Open an Azure DevOps work item in the web UI.
2. Upload an image into the work item description so Azure DevOps stores it as a work item attachment.
3. Save the work item and confirm that the image renders inline in the Azure DevOps web UI.
4. Open the same work item in the built-in Azure DevOps canvas in the GitHub Copilot app.
5. Observe the broken-image icon and alt text instead of the image.

### Expected behavior

Authenticated Azure DevOps attachment images embedded in a work item description should render inline in the canvas, matching the Azure DevOps web UI.

### Additional context

This appears specific to protected Azure DevOps attachment URLs. The canvas can render the surrounding rich text, but its image request may not use the Azure DevOps extension's authenticated request path.

#### Example failing image reference

```markdown
```

The failing source is a direct authenticated `_apis/wit/attachments/{id}` URL without a public access token or query string. The organization, project ID, and attachment ID are redacted because this is a public issue.

Start in the Azure DevOps canvas rendering path and trace how the markdown image URL for _apis/wit/attachments/{id} is requested. Compare that request with the Azure DevOps extension's authenticated request path; done means protected attachment images render inline in the canvas, matching the Azure DevOps web UI, without breaking surrounding rich text.

索引モデルが issue の本文から書いたものです。