feat: add nav bar button to publish pending config changes

Shows an orange "Publish Config" button to the left of the alert-pie
for admin users when there are staged config changes. Uses localStorage
to persist staged changes across page navigations so the button appears
on any page, not just settings.

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

hbd/server/templates/head.html

@@ -125,6 +125,23 @@
         .nav-links a { margin-right: 0; padding: 6px 0; font-size: 1em; }
       }
 
+      /* Pending config publish button */
+      .nav-publish-btn {
+        background: #e65100;
+        color: #fff;
+        border: none;
+        border-radius: 4px;
+        padding: 4px 10px;
+        font-size: 0.82em;
+        font-weight: 600;
+        cursor: pointer;
+        flex-shrink: 0;
+        white-space: nowrap;
+        margin-left: auto;
+      }
+      .nav-publish-btn:hover { background: #bf360c; }
+      .nav-publish-btn:disabled { opacity: 0.7; cursor: default; }
+
       /* Swiss railway clock — nav */
       .nav-pie {
         flex-shrink: 0;