Publish CLAUDE.md snapshot at /CLAUDE.md, linked from footers

Serve it as text/plain on deploy so browsers display the raw text
instead of downloading; add .dockerignore so local image builds can't
ship stale _site or host node_modules.

_includes/base.njk

@@ -26,6 +26,7 @@
       <a href="/about/">about</a>
       <a href="/code/">code</a>
       <a href="/subjects/">subjects</a>
+      <a href="/CLAUDE.md" target="_blank" rel="noopener">(CLAUDE.md)</a>
     </nav>
   </footer>
 </body>