Hide 'SANDS Portal' suffix on mobile nav bar

On screens < 600px the nav brand shrinks from 'ARK SANDS Portal' to
just 'ARK' via display:none on the .brand-suffix span. Also tightens
nav padding/gap on small screens.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: JihaoXin

website/dashboard/templates/app.html

@@ -370,6 +370,8 @@
       .detail-grid { grid-template-columns: 1fr; }
       .form-row { grid-template-columns: 1fr; }
       .modal { padding: 24px; }
+      .nav-brand .brand-suffix { display: none; }
+      nav { padding: 0 12px; gap: 8px; }
     }
 
     /* ── hero creation card ── */
@@ -559,7 +561,7 @@
 
 <!-- NAV -->
 <nav id="main-nav" style="display:none">
-  <a class="nav-brand" href="{{ app_base }}/#" onclick="event.preventDefault();navigate('dashboard')"><span>ARK</span> SANDS Portal</a>
+  <a class="nav-brand" href="{{ app_base }}/#" onclick="event.preventDefault();navigate('dashboard')"><span>ARK</span><span class="brand-suffix"> SANDS Portal</span></a>
   <span id="nav-admin-link" style="display:none"></span>
   <a href="{{ app_base }}/#feedback" onclick="event.preventDefault();navigate('feedback')"
      style="font-size:.85rem;font-weight:600;color:var(--text-second);text-decoration:none;padding:4px 10px;border-radius:6px;border:1px solid var(--border)">