PR previews: Netlify's own comment links to a 404, and the working preview has no lecture links #174

Previews build and deploy correctly here: on #170 the preview's pandas_panel.html shows the PR's new sentence. Two problems remain for a reviewer.

1. A broken link comes first. Netlify's own app comments on each PR ("Deploy Preview for majestic-griffin-10b166 ready!"), and its deploy-preview-N link returns 404 (checked 2026-10-23 on 🌐 [translation-sync] [pandas_panel] Describe the single .replace() call, not a loop #170). The working preview is the later github-actions comment ("🚀 Deployed on …"). Turn off deploy previews for this site in Netlify's settings, so the CI deploy is the only one.
2. The working comment has no lecture links. It gives a per-commit URL only. quantecon/actions/preview-netlify@v0.12.0, which QuantEcon/lecture-python-programming.fr uses, posts a stable pr-N URL and a link to each lecture the PR changes (checked on Update need_for_speed.md lecture-python-programming.fr#94). Switching needs pull-requests: write on the job and a Node setup step, as in the fr ci.yml.

ci.yml builds HTML only, so its first build reads every source and writes every page. If a notebook build is ever added before the HTML build, also clear _build/html after the cache download (rm -rf _build/.doctrees _build/html, as in QuantEcon/lecture-python.zh-cn's publish.yml). Otherwise the HTML build writes no pages and previews show the cached ones.

Done when

• Each PR carries one preview link, and it works.
• The preview comment links to each lecture the PR changes.