feat: Add variation-level license duration to product editor

- Added license_duration_days field to ProductVariant type
- Added License Duration input to each variation card
- Backend: ProductsController saves/loads variation-level _license_duration_days meta
- Allows different license periods per variation (e.g., 1-year, 2-year, lifetime)

admin-spa/src/routes/Products/partials/tabs/VariationsTab.tsx

@@ -22,6 +22,7 @@ export type ProductVariant = {
   manage_stock?: boolean;
   stock_status?: 'instock' | 'outofstock' | 'onbackorder';
   image?: string;
+  license_duration_days?: string;
 };
 
 type VariationsTabProps = {
@@ -43,10 +44,10 @@ export function VariationsTab({
 }: VariationsTabProps) {
   const store = getStoreCurrency();
   const [copiedLink, setCopiedLink] = useState<string | null>(null);
-  
+
   const siteUrl = window.location.origin;
   const spaPagePath = '/store';
-  
+
   const generateLink = (variationId: number, redirect: 'cart' | 'checkout' = 'cart') => {
     if (!productId) return '';
     const params = new URLSearchParams();
@@ -55,7 +56,7 @@ export function VariationsTab({
     params.set('redirect', redirect);
     return `${siteUrl}${spaPagePath}?${params.toString()}`;
   };
-  
+
   const copyToClipboard = async (link: string, label: string) => {
     try {
       await navigator.clipboard.writeText(link);
@@ -66,7 +67,7 @@ export function VariationsTab({
       toast.error('Failed to copy link');
     }
   };
-  
+
   const addAttribute = () => {
     setAttributes([...attributes, { name: '', options: [], variation: false }]);
   };
@@ -83,7 +84,7 @@ export function VariationsTab({
 
   const generateVariations = () => {
     const variationAttrs = attributes.filter(attr => attr.variation && attr.options.length > 0);
-    
+
     if (variationAttrs.length === 0) {
       toast.warning(__('Please add at least one variation attribute with options'));
       return;
@@ -276,6 +277,26 @@ export function VariationsTab({
                         )}
                       </div>
                     </div>
+
+                    {/* License Duration - only show if licensing is enabled on product */}
+                    <div className="col-span-2 md:col-span-4">
+                      <Label className="text-xs">{__('License Duration (Days)')}</Label>
+                      <Input
+                        type="number"
+                        min="0"
+                        placeholder={__('Leave empty to use product default')}
+                        value={variation.license_duration_days || ''}
+                        onChange={(e) => {
+                          const updated = [...variations];
+                          updated[index].license_duration_days = e.target.value;
+                          setVariations(updated);
+                        }}
+                        className="mt-1"
+                      />
+                      <p className="text-xs text-muted-foreground mt-1">
+                        {__('Override license duration for this variation. 0 = never expires.')}
+                      </p>
+                    </div>
                     <div className="grid grid-cols-2 md:grid-cols-4 gap-3">
                       <Input
                         placeholder={__('SKU')}
@@ -331,7 +352,7 @@ export function VariationsTab({
                         }}
                       />
                     </div>
-                    
+
                     {/* Direct Cart Links */}
                     {productId && variation.id && (
                       <div className="mt-4 pt-4 border-t space-y-2">