mirror "harness" etymology footnote onto GDG deck slide 13

Adds the same Old French etymology line ("The origin is Old French
harneis — gear, equipment, armor.") that was added to the canonical
best-practice deck, so the horse-harness analogy slide reads
identically across both decks. The line sits below the existing red
subtitle as a muted footnote (0.95rem, #666), with `text-align:
center` added for this deck because the GDG caption block relies on
flex centering rather than inherited text alignment.

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

presentation/2026-04-25-gdg-kolachi-cli-claude-code-gemini/index.html

@@ -772,6 +772,7 @@
             <!-- One-liner — kept, placed below the diagram -->
             <p style="font-size: 1.8rem; font-weight: 700; color: #1a1a1a; margin: 12px 0 6px; letter-spacing: -0.02em; line-height: 1.2;">A horse harness. A model harness.</p>
             <p style="font-size: 1.2rem; font-weight: 400; color: #C0392B; margin: 0; letter-spacing: 0.01em;">The model is the horse. Raw power, no direction. The harness is everything else.</p>
+            <p style="font-size: 0.95rem; font-weight: 400; color: #666; margin: 16px 0 0; letter-spacing: 0.01em; text-align: center;">The origin is Old French <em>harneis</em> &mdash; gear, equipment, armor.</p>
 
         </div>
     </div>