Feature Request: Archive/pin sessions in VS Code sidebar

Feature Request

Problem: The session sidebar in the VS Code extension gets cluttered quickly with old chats. There's no way to hide sessions you're done with while still keeping them accessible if needed later.

Current workaround: Delete old sessions or scroll past them. Neither is ideal — deleting loses context, and a long list makes it hard to find active work.

Proposed solution: Add an archive (or hide) option for sessions in the sidebar. Archived sessions would be hidden from the default view but accessible through a filter or "Archived" section. Optionally, allow pinning important sessions to the top.

Use case: Users who run many sessions per day (across projects, topics, and tools) need a way to keep their sidebar focused on active work without permanently losing past conversations.