fix(catalog): descarga de plantilla de precios proveedor con token

El enlace <a> a /pos/api/supplier-catalog/prices/template fallaba con 401
porque la navegación normal no envía el header Authorization. Se reemplaza
por un botón que descarga el blob vía fetch con Bearer token y dispara la
descarga del cliente. También se corrige clase btn-primary -> btn--primary.

pos/static/js/catalog.js

@@ -2148,6 +2148,31 @@
         }
     }
 
+    async function downloadPriceTemplate() {
+        try {
+            var res = await fetch('/pos/api/supplier-catalog/prices/template', {
+                headers: { 'Authorization': 'Bearer ' + token }
+            });
+            if (!res.ok) {
+                var data = await res.json().catch(function() { return {}; });
+                if (uploadPricesStatus) uploadPricesStatus.innerHTML = '<span style="color:var(--color-error);">' + esc(data.error || 'Error al descargar plantilla') + '</span>';
+                return;
+            }
+            var blob = await res.blob();
+            var url = URL.createObjectURL(blob);
+            var a = document.createElement('a');
+            a.href = url;
+            a.download = 'supplier_prices_template.csv';
+            document.body.appendChild(a);
+            a.click();
+            a.remove();
+            URL.revokeObjectURL(url);
+            if (uploadPricesStatus) uploadPricesStatus.innerHTML = '<span style="color:var(--color-success);">✓ Plantilla descargada.</span>';
+        } catch (e) {
+            if (uploadPricesStatus) uploadPricesStatus.innerHTML = '<span style="color:var(--color-error);">Error de red: ' + esc(e.message) + '</span>';
+        }
+    }
+
     function shouldShowUploadPricesButton() {
         try {
             var user = JSON.parse(localStorage.getItem('pos_employee') || '{}');
@@ -2180,6 +2205,7 @@
         openUploadPricesModal: openUploadPricesModal,
         closeUploadPricesModal: closeUploadPricesModal,
         submitUploadPrices: submitUploadPrices,
+        downloadPriceTemplate: downloadPriceTemplate,
     };
 
     // ─── INIT ───