Share Local sessions accross different GH Copilot CLI instances

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

I would like to start a session on a machine, and be able to load it / continue working on the session on another machine

### Proposed solution

I don't have a technical solution for that, but the idea is that Local sessions are also available accross different environments / machines.

### Example prompts or workflows

I am working on a project:
- I have few sessions from a machnie
- I move to my remote environment or another machine - I would like to look back at the other sessions I had on that project / repo

### Additional context

_No response_

No files, tests, or entry points are identified. Start by locating how the CLI stores and discovers local sessions, then define how a session created on one machine can be listed and continued on another and verify that workflow end to end.

Written by the indexing model from the issue text.