What would you like to be added?

The /export command is available in the CLI but not in the VSCode Companion. I want to be able to export my chat session history to a file directly from the IDE.

In the CLI, /export <format> supports four formats: HTML, Markdown, JSON, and JSONL.

The VSCode Companion should support the same functionality. For UX:

• /export with no argument should default to HTML (the most common and useful format), so users can simply select the command and go
• Other formats (/export md, /export json, /export jsonl) should be documented in the slash command description shown in the completion menu, so users can discover them without extra UI
• The IDE experience should feel native:
  • A Save As dialog for choosing the file destination and name, instead of silently writing to the working directory
  • A notification after export with an "Open File" action, so the user can quickly view the result

Why is this needed?

When working in VSCode, I have to switch to a terminal to export my conversation history. This is useful for:

• Saving important technical discussions for documentation
• Sharing conversation context with teammates
• Keeping a record of decisions made during a coding session

Additional context

Related to the broader effort of achieving feature parity between CLI and VSCode Companion:

• Allow toggling Plan Mode in VSCode Companion #1985 (Plan Mode in VSCode Companion)
• Improve Slash Command Behavior in VSCode Companion #1990 (Slash Command Behavior in VSCode Companion)