fix(loyalty): open View Merchant link in new tab to preserve loyalty context

The "View Merchant" quick action on the loyalty merchant detail hub
links to the tenancy merchant page, which has its own back button going
to /admin/merchants. Opening in a new tab prevents losing the loyalty
context. Added external link icon as visual indicator.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/templates/loyalty/admin/merchant-detail.html

@@ -42,9 +42,11 @@
             </a>
             <a
                 :href="`/admin/merchants/${merchant?.id}`"
+                target="_blank"
                 class="flex items-center px-4 py-2 text-sm font-medium leading-5 text-gray-700 transition-colors duration-150 bg-gray-100 border border-gray-300 rounded-lg hover:bg-gray-200 dark:bg-gray-700 dark:text-gray-300 dark:border-gray-600 dark:hover:bg-gray-600">
                 <span x-html="$icon('building-office', 'w-4 h-4 mr-2')"></span>
                 {{ _('loyalty.admin.merchant_detail.view_merchant') }}
+                <span x-html="$icon('arrow-top-right-on-square', 'w-3 h-3 ml-1 opacity-50')"></span>
             </a>
             <a x-show="program"
                 :href="`/admin/loyalty/merchants/${merchantId}/cards`"