Cmd+A (Select All) does not work in canvas side panels on macOS

### Short summary

Cmd+A (Select All) does nothing when focus is in a canvas side panel on macOS.

### Affected version or release

Copilot app, macOS (Darwin). Version not captured at the time of the report.

### Installation context

Local desktop app, canvas side panel open next to a project session.

### What happened?

While viewing content in a canvas side panel, I pressed **Cmd+A** to select the page contents so I could copy them. Nothing was selected.

Manually drag-selecting the text with the mouse and then pressing **Cmd+C** works fine, so copying is possible — but for anything longer than a screen it's tedious and error-prone.

This looks like the app's native macOS **Edit** menu has no **Select All** item bound to Cmd+A, so the shortcut is never routed into the webview hosting the canvas. Drag-select and Cmd+C are native webview behaviors that work without a menu binding, which is consistent with only Cmd+A being broken.

### Steps to reproduce

1. On macOS, open the Copilot app.
2. Open any canvas in the side panel that renders a page of text/content.
3. Click into the canvas panel to give it focus.
4. Press **Cmd+A**.
5. Observe that nothing is selected.
6. Drag-select some text with the mouse and press **Cmd+C** — this works, confirming copy itself is functional.

### Expected behavior

Cmd+A should select the contents of the focused canvas panel, matching standard macOS behavior and the rest of the app. Cmd+A followed by Cmd+C should copy the panel's contents.

### Additional context

- Platform: macOS (Darwin)
- Only Cmd+A appears affected; mouse selection and Cmd+C behave normally.
- Likely fix is registering a **Select All** accelerator in the app's native Edit menu so the shortcut reaches the webview.

Commencez par reproduire le problème dans l’application Copilot sur macOS avec un panneau latéral de canvas ciblé, puis examinez la gestion native du menu Edit décrite dans le rapport. C’est terminé lorsque Cmd+A sélectionne le contenu du panneau ciblé et que Cmd+A suivi de Cmd+C le copie, tandis que la sélection à la souris et Cmd+C continuent de fonctionner.

Rédigé par le modèle d'indexation à partir du texte de l'issue.