Implement PreTeXt Document Outline sidebar pane

[harsharajkumar-273]

Build a collapsible logical textbook structure tree (chapter ➔ section ➔ exercises) in the Monaco Editor activity rail so authors can navigate large textbooks easily without relying solely on file names.

[sanket1035]

Hi @harsharajkumar-273 👋
I'd like to work on this issue. I've gone through the repo structure and understand the context here — I have experience with [React/Node/Express/Prisma/Docker — jo bhi relevant ho is issue ke liye] and can get started right away.
If assigned, I'll make sure to:
Follow the existing code style and architecture conventions
Add proper tests/validation where applicable
Keep the PR focused and well-documented with clear commit messages
I'll ensure the PR quality is excellent before requesting review. Please assign this to me — happy to share my approach in more detail if needed.
Thanks!

[github-actions]

Hi @sanket1035, you have been successfully assigned to this issue! Happy coding 🚀