Clickable home page stat cards; clean up nav; add buttons on list pages; move export/import to home

templates/device_list.html

@@ -5,6 +5,9 @@
 <h1>Devices</h1>
 
 <div class="card">
+  <div style="display:flex;justify-content:flex-start;margin-bottom:0.5rem;">
+    <a class="btn btn-primary btn-sm" href="{{ url_for('device_add') }}">+ Add Device</a>
+  </div>
   <div id="device-filter-bar" style="display:flex;gap:0.5rem;flex-wrap:wrap;align-items:center;margin-bottom:0.75rem;">
     <select id="filter-type" onchange="applyDeviceFilters()"
             style="padding:0.25rem 0.5rem;font-size:0.85rem;border:1px solid #cbd5e1;border-radius:4px;">