Feature request: Organize Copilot Chat sessions into folders and projects

## Problem

Copilot Chat sessions become difficult to manage as their number grows. Conversations related to different projects, features, bugs, and GitHub issues are shown together, making it difficult to find and continue previous discussions.

This is particularly challenging for long-running projects and when working across multiple repositories or workspaces.

## Proposed solution

Please add a way to organize Copilot Chat sessions into user-defined folders or projects.

Possible functionality:

- Create, rename, and delete folders or projects
- Move chat sessions between folders or projects
- Rename individual chat sessions
- Search and filter sessions by title, content, project, repository, or workspace
- Associate a chat session with a GitHub issue or pull request
- Optionally associate sessions with a VS Code workspace or repository
- Preserve the organization after restarting VS Code

The experience could be similar to ChatGPT Projects, while being integrated into the VS Code Chat Sessions view.

## Example workflow

I could create a project called `Feature_Request_1` and organize related conversations into folders such as:

- Requirements
- SQL development
- Debugging
- Testing
- Documentation

Individual chat sessions could optionally be linked to a GitHub issue or pull request.

## Benefits

This would make Copilot more useful for long-running development tasks, improve continuity between sessions, and make it easier to retrieve previous decisions and technical discussions.

## Related issues

This request is related to:

- #332166, which focuses on preserving chat history when project folders are moved or renamed
- #334228, which focuses on making chat sessions available across workspaces

Those issues address chat persistence and availability. This request focuses specifically on organizing chat sessions into folders or projects.

## Alternatives considered

Currently, users have to rely on chat titles, external notes, or manually saved transcripts. These approaches do not provide a structured way to manage related conversations.