feat: render code blocks in markdown

[Hellebore]

• Render markdown response from AI into html, apply syntax highlighting and sanitize
• Remaining issues are the scrollbar not being right and handling theme changes - will handle these separately

Checklist

• [ ] If package.json or yarn.lock have changed, then test the VSIX built by yarn run vsce package works from a direct install

[Hellebore]

It's looking nice!

Here's a few things I've spotted:

• Bullet points appear outside the chat bubble, and headers seems pretty big
• When generating code wider than the sidebar it scrolls to the right
• I seem to have different themes in different code blocks - check the background colours
• Is it possible to use the theme of vscode? Mine chat code looks totally different from the editor
• Just code on it's own looks a little funny
• I'd expect when I click a recipe button that it displays as a user message rather than a assistant message. e.g. Run recipe - generate unit tests

Good points - have created a new issue for these