fix(navigation): Normalize default menu button color

Render navigation menu buttons with the secondary ghost style when their
color is unset or set to the default choice.

This fixes plugin menu buttons, which default to "default" rather than
None, while preserving explicitly configured button colors.

netbox/utilities/templates/navigation/menu.html

@@ -45,7 +45,7 @@
                   {% if buttons %}
                     <div class="dropdown-item-buttons d-inline-flex ms-1">
                       {% for button in buttons %}
-                        <a href="{{ button.url }}" class="btn btn-sm btn-ghost btn-{{ button.color|default:"secondary" }} px-2" title="{{ button.title }}" aria-label="{{ button.title }}">
+                        <a href="{{ button.url }}" class="btn btn-sm btn-ghost btn-{% if button.color and button.color != 'default' %}{{ button.color }}{% else %}secondary{% endif %} px-2" title="{{ button.title }}" aria-label="{{ button.title }}">
                           <i class="{{ button.icon_class }}" aria-hidden="true"></i>
                         </a>
                       {% endfor %}