hotkeys: 'd' toggles demo mode

Saves a click during live demos. Topbar tooltip updated to mention
the binding. Hotkey is gated by the same input-focus check as 'c' /
arrow keys, so typing 'd' in a search box won't fire it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

training/dashboard/static/dashboard.js

@@ -188,6 +188,7 @@
       case 'Home': e.preventDefault(); scrollToScene(0); break;
       case 'End':  e.preventDefault(); scrollToScene(scenes.length - 1); break;
       case 'c': case 'C': e.preventDefault(); setClickNav(!clickNavOn); break;
+      case 'd': case 'D': e.preventDefault(); setDemo(!demoActive); break;
     }
   });
   prevBtn.addEventListener('click', prev);

training/dashboard/static/index.html

@@ -1313,6 +1313,6 @@
     </article>
   </div>
 
-  <script src="/static/dashboard.js?v=b6877976"></script>
+  <script src="/static/dashboard.js?v=5316d1d8"></script>
 </body>
 </html>