ver. 0.303: Fix attribute display collision + product preview button

Fix: product attributes with the same sort order value were overwriting
each other in getProductAttributes(), causing only one attribute to
display on the frontend. Now uses usort() with sequential keys.

New: Preview button in product edit form opens product page in new tab.

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

admin/templates/components/form-edit.php

@@ -61,6 +61,10 @@ $_SESSION['can_use_rfm'] = true;
               <a href="<?= htmlspecialchars($action->url) ?>" class="btn btn-dark btn-sm" id="g-edit-cancel">
                 <i class="fa fa-reply mr5"></i>Wstecz
               </a>
+            <?php elseif ($action->name === 'preview'): ?>
+              <a href="<?= htmlspecialchars($action->url) ?>" class="btn btn-info btn-sm" target="_blank">
+                <i class="fa fa-eye mr5"></i><?= htmlspecialchars($action->label) ?>
+              </a>
             <?php else: ?>
               <a href="<?= htmlspecialchars($action->url) ?>" class="btn <?= htmlspecialchars($action->cssClass) ?> btn-sm">
                 <?= htmlspecialchars($action->label) ?>