Add Foundation page with accessible (PDF/UA-1) core documents

Publishes the seven foundational documents — mission, vision, core values,
whitepaper (The Adoption Gap), manifesto, operating principles, and company
overview — as a brand-styled /foundation/ page plus downloadable PDF/UA-1
tagged PDFs. Adds a Foundation link to the homepage nav.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

index.html

@@ -41,6 +41,7 @@
       <div class="nav-links">
         <a href="#focus">Focus</a>
         <a href="#approach">Approach</a>
+        <a href="foundation/">Foundation</a>
         <a href="#contact">Contact</a>
         <a class="nav-pill" href="mailto:contact@houstonlabs.us">Email&nbsp;us</a>
       </div>