Implement TOC with navigation

First of all, thank you very much for this beautiful piece of software, it’s exactly what I did not know I needed. Glazing aside, I have a suggestion. I often work with long notebooks where I need to carefully divide the code and results into sections so they’ are easy to find later. Markdown headings already help a lot, especially with JupyterLab’s “Show heading number in the document” feature (see image). The heading numbers reflect the hierarchy and can be clicked to jump directly to that section. <img width="874" height="552" alt="Image" src="https://github.com/user-attachments/assets/444c2969-a808-4935-9b72-5f5a3199dd0d" /> Would you be interested in adding something similar to Euporie? The feature I imagine is a keyboard shortcut that opens a floating, navigable “table of contents” panel. It would display the auto-generated heading hierarchy, allow navigation with the arrow keys, and let the user press Enter to jump to the corresponding cell. If this seems useful, I would be happy to contribute a first attempt. Any pointers on where to start in the codebase would be greatly appreciated. Kind regards