fix: remap add-to-cart→product_id for AJAX, fallback zone detection for guest FSN amount

assets/js/floating-cart.js

@@ -113,7 +113,17 @@
 				e.preventDefault();
 				$btn.addClass( 'loading' ).data( 'cgkit-fc-handled', true );
 
-				$.post( ajaxUrl, $form.serialize() )
+				// WC's wc-ajax=add_to_cart reads $_POST['product_id'], but the
+				// single-product form submits the ID as field name 'add-to-cart'.
+				// Append the correctly-named field so the endpoint finds it.
+				var serialized = $form.serialize();
+				var productId  = $form.find( '[name="add-to-cart"]' ).val() ||
+				                 $form.find( '[name="product_id"]' ).val() || '';
+				if ( productId && serialized.indexOf( 'product_id=' ) === -1 ) {
+					serialized += '&product_id=' + encodeURIComponent( productId );
+				}
+
+				$.post( ajaxUrl, serialized )
 					.done( function ( response ) {
 						if ( ! response ) {
 							self.formFallback( $form, $btn );