fix(ci): deploy Sphinx docs to gh-pages for project Pages URL

[mathildepapillon]

Summary

The public URL https://geometric-intelligence.github.io/topobench/ is served from this repository’s gh-pages branch (project Pages), not from geometric-intelligence.github.io/topobench/. This PR deploys the Sphinx build to gh-pages using GITHUB_TOKEN, adds .nojekyll, fixes the github.repository guard to geometric-intelligence/topobench, and adds workflow_dispatch for manual redeploys.

After merge (maintainer checklist)

1. Settings → Actions → General → Workflow permissions: set Read and write so GITHUB_TOKEN can push gh-pages (if not already).
2. Confirm Settings → Pages uses gh-pages branch, / (root).
3. Open Actions → Docs: Check and Deploy for the merge commit and wait until it succeeds (or use Run workflow).
4. Verify the site: Sphinx/pydata layout at https://geometric-intelligence.github.io/topobench/ and https://geometric-intelligence.github.io/topobench/.nojekyll returns 200.

Test plan

• Merge PR, confirm docs workflow is green on main.
• Spot-check docs homepage and a challenge subpage after deploy.

Made with Cursor

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.03%. Comparing base (04a409c) to head (28f3241).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #348   +/-   ##
=======================================
  Coverage   94.03%   94.03%           
=======================================
  Files         206      206           
  Lines        8732     8732           
=======================================
  Hits         8211     8211           
  Misses        521      521           

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