docs(pages): SEO setup + Cayman design pass

_config.yml:
- canonical url/baseurl for jekyll-seo-tag + jekyll-sitemap
- jekyll-seo-tag + jekyll-sitemap plugins; og:image link-preview card
- keep the raw engineering record (dev/ finding log, per-level status,
  triage notes) out of sitemap.xml; keep the two linked dev/ docs in

_includes/head-custom.html:
- Google/Bing Search Console verification tags
- full design pass over the stock Cayman theme: IBM Plex Sans/Mono,
  restrained amber-on-slate palette, light + dark themes, faded
  attract-mode screenshot header treatment, tightened typographic
  hierarchy, dark code blocks, quieter tables

docs/_config.yml

@@ -8,9 +8,44 @@ description: >-
 theme: jekyll-theme-cayman
 show_downloads: false
 
+# Canonical site location - used by jekyll-seo-tag (canonical URLs, og: tags)
+# and jekyll-sitemap (absolute URLs in sitemap.xml).
+url: https://jkdansereau.github.io
+baseurl: /goldeneye-pc-port
+
+# Link-preview card image for jekyll-seo-tag (og:image / twitter:image).
+# Path is relative to the site root; the plugin prepends url + baseurl.
+image: /img/attract-bunker1.png
+
+# Both are on the GitHub Pages plugin whitelist - no Gemfile needed.
+# jekyll-seo-tag: per-page <title>/description/canonical/OpenGraph via {% seo %}
+#   (already emitted by the Cayman layout).
+# jekyll-sitemap: generates /sitemap.xml for Search Console / Bing submission.
+plugins:
+  - jekyll-seo-tag
+  - jekyll-sitemap
+
 # jekyll-relative-links (on by default for Pages) rewrites the .md links in
 # these docs to .html so cross-links work on the published site.
 
 # Rolling local working files - not useful as published pages.
 exclude:
   - HANDOFF.md
+
+# Keep the raw engineering record (finding log, per-level status, triage
+# notes, backlogs) out of sitemap.xml so search engines aren't steered at it.
+# The pages still build and stay reachable from cross-links; the two dev/
+# docs that are linked from the site index are kept in.
+defaults:
+  - scope:
+      path: "dev"
+    values:
+      sitemap: false
+  - scope:
+      path: "dev/agentic-development.md"
+    values:
+      sitemap: true
+  - scope:
+      path: "dev/game-behavior-reference.md"
+    values:
+      sitemap: true