Share and persist Chat sessions across CLI, Visual Studio, and Copilot Desktop

### Feature summary

Cross-Interface Chat Session Persistence and Synchronization

### What problem are you trying to solve?

Right now, the GitHub Copilot experience feels fragmented across different environments. If I start a complex troubleshooting or refactoring session using Copilot in the CLI (gh copilot) or inside Visual Studio, that context and history are lost if I want to switch over to the dedicated Copilot Desktop app to continue the conversation.

### Proposed solution

I would like a unified session history. Specifically:

Cross-Interface Visibility: Any active or past chat session started in Visual Studio or the GitHub CLI should appear in the Copilot Desktop app's history sidebar.

Context Continuity: Opening a CLI or Visual Studio session inside the Desktop app should preserve the full conversation history so I can pick up right where I left off.

Describe alternatives you've considered
Manually copying and pasting prompts and previous assistant responses from the terminal or IDE into the Desktop app, which breaks the development workflow.

Additional context
This would bridge the gap between headless terminal workflows, heavy IDE usage, and the standalone desktop chat experience, making Copilot feel like a singular, omnipresent assistant.

Why this helps:
Using terms like "Sync," "Unified," or "Persist" helps the team categorize it under their account-level or sync features.

Specifying "Context Continuity" highlights the actual pain point—it's not just about seeing a list of past chats, it's about keeping the momentum of your coding session.

### Workflow impact

Workflow Continuity: Allow a developer to start a troubleshooting or refactoring conversation in a lightweight interface (like the CLI or inline IDE chat) and instantly pick up the exact same session inside the dedicated Desktop app with full context preserved.

### Installation context

_No response_

### Additional context

_No response_