chore(workflows): add PR HTML validation job + inline comments to Pages workflow

[Rudra00codes]

Summary

Add a lightweight pull-request validation job to the GitHub Pages workflow to run HTML validation across contributor pages, and include a few brief inline comments in the workflow for clarity. This helps catch broken HTML/link problems earlier (on PRs) without changing the existing build & deploy behaviour.

What changed

Updated .github/workflows/jekyll-gh-pages.yml:

• Added a validate job that runs on pull_request events and executes html-validate against web/pages/**/*.html.
• Inserted short YAML comments to explain concurrency and the validate job intent.
• Left existing build and deploy jobs intact (deploy still runs only on push).

Why

• Many contributor pages are plain HTML and may contain accidental syntax or linking issues. Running an HTML validation step on PRs prevents these from reaching the deployed site and reduces review friction.
• The inline comments make the workflow easier to understand for contributors and maintainers.

How to test (locally)

1. From the repo root, install html-validate (Node + npm required):

   npm ci --no-audit --no-fund || true
   npm install --no-audit --no-fund html-validate@9

2. Run the validator against the pages:

   npx html-validate --severity error "web/pages/**/*.html"

   Note: The workflow currently runs install/run guarded with || true for the install step to avoid failing when no package.json file exists; locally, you can run the commands above and see the actual failures.

Files changed

• .github/workflows/jekyll-gh-pages.yml — added validate job + comments