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/hugo.toml

@@ -0,0 +1,42 @@
+baseURL = "https://blog.xsltplayground.com/"
+languageCode = "en-us"
+title = "XSLT Playground"
+
+publishDir = "../docs"
+enableRobotsTXT = true
+
+[pagination]
+pagerSize = 10
+
+[params]
+subtitle = "Online XSLT editor built for real-world transformations."
+lead = "Run and debug XSLT online with multi-parameter inputs, timing hints, and fast feedback. This site hosts release notes, guides, and deployment options for XSLT Playground."
+
+[params.adsense]
+# Prefer setting ADSENSE_CLIENT and ADSENSE_INARTICLE_SLOT env vars when building if you don't want the values committed.
+client = "ca-pub-1549720748100858"
+inArticleSlot = ""
+
+[params.ethicalads]
+publisher = "xsltplaygroundcom"
+
+[menu]
+  [[menu.main]]
+  name = "Home"
+  url = "/"
+  weight = 1
+
+  [[menu.main]]
+  name = "Posts"
+  url = "/posts/"
+  weight = 2
+
+  [[menu.main]]
+  name = "About"
+  url = "/about/"
+  weight = 3
+
+  [[menu.main]]
+  name = "Charts"
+  url = "https://alexandrev.github.io/xslt-lab/index.yaml"
+  weight = 4