feat(badges): wire duplex field — hide badge back for single-sided templates

- Add duplex + style_href to properties_to_save so they're cached in IDB
- Derive show_badge_back: true when duplex is null/unset (safe default for
  existing templates) or 1; false when duplex=0 (single-sided, e.g. Axonius
  NYC using Zebra ZC10L PVC cards)
- Wrap entire badge_back section in {#if show_badge_back} so the DOM node
  is fully removed rather than just hidden — cleaner than a CSS class approach

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

src/lib/ae_events/ae_events__event_badge_template.ts

@@ -35,6 +35,8 @@ export const properties_to_save = [
     'show_qr_back',
     'layout',
     'style_filename',
+    'style_href',
+    'duplex',
     'enable',
     'hide',
     'priority',

src/routes/events/[event_id]/(badges)/badges/[badge_id]/ae_comp__badge_obj_view.svelte

@@ -78,6 +78,12 @@
         }
     });
 
+    // Show the badge back section when duplex=1 (or when duplex is not yet set, as a safe default).
+    // duplex=0/false → single-sided print (e.g. Zebra ZC10L PVC cards); back section is hidden.
+    let show_badge_back = $derived(
+        $lq__event_badge_template_obj?.duplex == null || !!$lq__event_badge_template_obj?.duplex
+    );
+
     // *** Set initial variables
     $effect(() => {
         $slct.event_badge_id = event_badge_id; // $page['page_for']['event_badge_id'];
@@ -1066,6 +1072,8 @@ onkeypress={() => {
         <!-- *** badge section end *** -->
 
         <!-- *** badge_back (fold under) section start *** -->
+        <!-- duplex=0 on the template hides this entire section (single-sided print) -->
+        {#if show_badge_back}
         <section
             class="badge_back
         flex flex-col gap-1
@@ -1408,6 +1416,7 @@ onkeypress={() => {
             <!-- </div> -->
             <!-- fold class div end -->
         </section>
+        {/if}
         <!-- *** fold under section end *** -->
 
         <!-- *** receipt section start *** -->