Set up development environment (Ruby 3.2 / Jekyll)

[lukepan-99]

Summary

Sets up the development environment for this Jekyll + reveal.js slideshow so it builds and runs on the current toolchain.

• Regenerated Gemfile.lock for Ruby 3.2. The original lock pinned nokogiri 1.11.3 / jekyll 3.9.0, which only support Ruby < 3.1 and fail to install on Ruby 3.2. It now resolves to github-pages 232 / jekyll 3.10.0 (which includes webrick, required on Ruby 3.x). The Gemfile constraint (github-pages >= 207) is unchanged.
• Added AGENTS.md with a ## Cursor Cloud specific instructions section documenting how to run the dev server, the lint/link-check command, and non-obvious gotchas.

Verification

• bundle install / bundle exec jekyll build succeed.
• bundle exec jekyll serve --host 0.0.0.0 --port 4000 serves the slideshow (HTTP 200) at http://localhost:4000/.
• bundle exec htmlproofer _site/index.html --disable-external --ignore-empty-alt passes.
• Verified the slideshow renders and navigates in the browser (a temporary demo slide was used only for the navigation demo and is not committed).

jekyll_slideshow_navigation_demo.mp4

Welcome slide
Hello World slide

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