[codex] Update GitHub Pages security dependencies

[gustavByte]

What changed

• refreshed Gemfile.lock by updating the github-pages and html-proofer dependency stack
• upgraded vulnerable transitive gems including addressable to 2.9.0, activesupport to 8.1.3, nokogiri to 1.19.2, commonmarker to 0.23.12, and tzinfo to 2.0.6

Why

• GitHub Dependabot flagged multiple vulnerable Ruby gems in this repository, including addressable (CVE-2026-35611)
• this repo already allowed newer github-pages versions in Gemfile, so regenerating the lockfile was the smallest repo-only fix that removed several outdated transitive dependencies at once

Validation

• ran bundle update github-pages html-proofer in WSL with a repo-local Bundler path
• ran bundle exec jekyll build