Add link back to main app in dashboard header

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/public/dashboard.html

@@ -121,6 +121,7 @@ a { color: var(--cool); text-decoration: none; }
   </div>
   <div class="header-right">
     <span class="station-name" id="stationName"></span>
+    <a href="/" class="logout">App</a>
     <a href="/dashboard/logout" class="logout">Sign out</a>
   </div>
 </div>