feat: click TOC entries to jump to section

[giovannipapini]

Summary

• Stores the rendered TOC panel rect in app.toc_area (same pattern as content_area)
• Builds a toc_display_to_toc_index map inside refresh_toc_cache so each visible display row maps back to its toc entry
• Adds scroll_to_toc_display_line(display_idx) on App
• In the mouse handler, a left-click inside the TOC list area (below the header) calls that method to jump to the section

Test plan

• Open a Markdown file with multiple headings and press t to show the TOC
• Click a level-1 heading entry — document jumps to that section
• Click a level-2 sub-entry — document jumps to that sub-section
• Click the "TABLE OF CONTENTS" header row — nothing happens
• Clicking the right-border column of the TOC panel — nothing happens
• Numkey (1–9) navigation still works unchanged

Closes #183

[RivoLink]

Hi @giovannipapini
Thanks for your interest in the project and for your PR, I really appreciate it.

A couple of requests:

• Squash into a single commit as feat: toc mouse navigation and please remove Claude as co-author.
• Signed commit: GPG signing is required on main. If you can sign it, great. If not, no worries, I'll handle it and preserve you as author.

GPG signing docs : https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits

[giovannipapini]

Hi @RivoLink, thanks for the review! All done:

• Squashed into a single commit titled feat: toc mouse navigation
• Removed Claude as co-author (and dropped the Claude line from the PR description)
• Signed the commit — it now shows as Verified on GitHub

Ready for another look whenever you have a moment.

[RivoLink]

Hi,
It’s perfect, thank you so much 😊

[RivoLink]

No worries about the cargo audit.
It’s not related to your update, I’ll fix it.

[RivoLink]

I’m on it. I may need you to rebase after my fix.
Sorry, it’s my bad.

[RivoLink]

Hi @giovannipapini
Can you rebase the branch from main to fix the Cargo audit issue in CI?

[RivoLink]

Perfect, thank you so much 😊

[RivoLink]

Nice 😊