fix: Correct preview response data access

Fixed double .data access in template preview:
- Changed response.data.data.rendered_html
- To response.data.rendered_html

templateService already returns response.data, no need to access .data twice.

frontend/src/pages/Templates.jsx

@@ -231,7 +231,7 @@ function Templates() {
         company_name: companyPlaceholder,
         employee_name: employeePlaceholder,
       });
-      const renderedHtml = response.data.data.rendered_html;
+      const renderedHtml = response.data.rendered_html; // Fixed: removed extra .data
       setPreviewHtml(renderedHtml);
       if (previewUrl) {
         URL.revokeObjectURL(previewUrl);