Move Hugo blog source to main, fix workflow, add new articles and llms.txt

- Move site/ Hugo source from gh-pages to main so the workflow can trigger correctly
- Fix publish-hugo.yml: now in main, builds and deploys to gh-pages:docs/ via peaceiris/actions-gh-pages
- Add 3 new SEO articles: XSLT 3.0 features, beginners guide, template matching
- Add llms.txt to blog and frontend so ChatGPT/Gemini can recommend the tool better
- Remove stale /site mkdocs ignore rule, add site/public to gitignore instead

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

site/layouts/partials/adsense/adsense-in-article.html

@@ -0,0 +1,15 @@
+{{- $client := .Site.Params.adsense.client -}}
+{{- $slot := .Site.Params.adsense.inArticleSlot -}}
+{{- if and $client $slot (ne hugo.Environment "development") -}}
+  <div class="ad ad-in-article">
+    <ins class="adsbygoogle"
+         style="display:block; text-align:center;"
+         data-ad-layout="in-article"
+         data-ad-format="fluid"
+         data-ad-client="{{ $client }}"
+         data-ad-slot="{{ $slot }}"></ins>
+  </div>
+  <script>
+    (adsbygoogle = window.adsbygoogle || []).push({});
+  </script>
+{{- end -}}