Cross-app session sync between Copilot CLI and Copilot Desktop App

### Describe the feature or problem you'd like to solve

I use both the GitHub Copilot CLI and the Copilot desktop app on macOS. Currently, sessions started in the CLI are not visible or accessible in the desktop app, and vice versa. It would be very useful to have sessions synced (or at least importable/resumable) across both interfaces, so I can seamlessly switch between a terminal and desktop workflow without losing context. Suggested improvements: • Show CLI sessions in the desktop app's session list • Allow resuming a CLI session from the desktop app (and vice versa) • Or at minimum, a one-click export/import between the two

### Proposed solution

_No response_

### Example prompts or workflows

_No response_

### Additional context

_No response_

Start with the Copilot CLI session and resume entry points and the desktop app's session list on macOS. Compare how each interface exposes sessions, then determine whether synchronization or one-click import/export best fits the workflow. Done means a session can be discovered and resumed across both interfaces, or transferred between them.

Written by the indexing model from the issue text.