docs(manual): chapters for the remaining seven actions, and delete QUICK-REFERENCE.md

[quantecon-services]

PR 3 of the user manual (#178). It uses the generator and chapter template from PR 2; see #178, decisions 3–5.

• Chapters under docs/user/actions/ for build-lectures, build-jupyter-cache, restore-jupyter-cache, preview-netlify, preview-cloudflare, publish-gh-pages and deploy-cloudflare, each with a generated signpost README.
• Move README-only content into the chapters:
  • the Netlify and Cloudflare setup guides and the Cloudflare vs Netlify comparison;
  • the publish-gh-pages migration notes;
  • the deploy-cloudflare Access checklist, with no account details.
• publish-gh-pages chapter: document the release assets (archive, SHA256 checksum, manifest) as a format consumers can rely on. This is the "compatibility contract" item from HTML Recovery Tool: Restore lecture sites from GitHub Release assets #27 that no longer has a home now docs: reconcile action READMEs and templates with the shipped code #109 is closed.
• Delete docs/QUICK-REFERENCE.md. Its one-screen table becomes docs/user/README.md.
• Enable the every-action-has-a-chapter check in the gate.

The deploy-cloudflare chapter describes main (require-access, as released in v0.12.0). #177 updates it with its own PR.