fix(css): scope final-cta grid to inner section-shell wrapper

Move display:grid and gap from .final-cta to .final-cta > .section-shell
so the grid context is applied to the correct container element, not the
outer section. Wrap final-cta content in index.html with a section-shell
div accordingly. Also fix .no-results bottom padding that was missing.

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

website/templates/index.html

@@ -243,7 +243,8 @@
   </div>
 </section>
 
-<section class="final-cta section-shell" data-reveal>
+<section class="final-cta" data-reveal>
+<div class="section-shell">
   <p class="section-label">Contribute</p>
   <h2>Know a project that belongs here?</h2>
   <p>Tell us what it does and why it stands out.</p>
@@ -263,5 +264,6 @@
       >Star the repository</a
     >
   </div>
+</div>
 </section>
 {% endblock %}