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/index.html

@@ -0,0 +1,42 @@
+{{ define "main" }}
+<section class="hero">
+  <p class="eyebrow">Online XSLT Editor</p>
+  <h1>{{ .Title }}</h1>
+  <p class="lead">{{ .Params.description | default .Site.Params.lead }}</p>
+  <div class="cta-row">
+    <a class="button" href="https://xsltplayground.com">Open the playground</a>
+    <a class="button ghost" href="{{ "/posts/" | relURL }}">Read updates</a>
+    <a class="button ghost" href="https://alexandrev.github.io/xslt-lab/index.yaml">Helm chart index</a>
+  </div>
+</section>
+
+<section class="grid">
+  <article class="card">
+    <p class="eyebrow">How the playground helps</p>
+    <h2>Built for real XSLT work</h2>
+    <p>Run XSLT online with multiple inputs and parameters, see results as you type, and get timing hints to spot regressions before they hit production.</p>
+    <ul class="checks">
+      <li>Multi-parameter transforms</li>
+      <li>Live execution and inline output</li>
+      <li>Timing to guide optimization</li>
+    </ul>
+  </article>
+  <article class="card">
+    <p class="eyebrow">Latest posts</p>
+    <h2>Recent updates</h2>
+    <ul class="post-list">
+      {{ $posts := first 3 (where .Site.RegularPages "Section" "posts") }}
+      {{ if gt (len $posts) 0 }}
+        {{ range $posts }}
+          <li>
+            <a href="{{ .RelPermalink }}">{{ .Title }}</a>
+            <span class="muted">{{ .Date.Format "02 Jan 2006" }}</span>
+          </li>
+        {{ end }}
+      {{ else }}
+        <li class="muted">No posts yet. Add more in <code>site/content/posts/</code>.</li>
+      {{ end }}
+    </ul>
+  </article>
+</section>
+{{ end }}