Fix orders link: use plain anchor for cross-domain cart navigation

The orders link was using links.link macro which adds hx-get, causing
htmx:invalidPath because cart.rose-ash.com is cross-origin. Use a
plain <a> tag for this cross-domain link instead.

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

templates/_types/auth/_nav.html

@@ -2,6 +2,8 @@
 {% call links.link(url_for('auth.newsletters'), hx_select_search, select_colours, True, aclass=styles.nav_button) %}
   newsletters
 {% endcall %}
-{% call links.link(cart_url('/orders/'), hx_select_search, select_colours, True, aclass=styles.nav_button) %}
-  orders
-{% endcall %}
+<div class="relative nav-group">
+  <a href="{{ cart_url('/orders/') }}" class="{{styles.nav_button}}">
+    orders
+  </a>
+</div>