feat: product page layout toggle (flat/card), fix email shortcode rendering

- Add layout_style setting (flat default) to product appearance
  - AppearanceController: sanitize & persist layout_style, add to default settings
  - Admin SPA: Layout Style select in Appearance > Product
  - Customer SPA: useEffect targets <main> bg-white in flat mode (full-width),
    card mode uses per-section white floating cards on gray background
  - Accordion sections styled per mode: flat=border-t dividers, card=white cards

- Fix email shortcode gaps (EmailRenderer, EmailManager)
  - Add missing variables: return_url, contact_url, account_url (alias),
    payment_error_reason, order_items_list (alias for order_items_table)
  - Fix customer_note extra_data key mismatch (note → customer_note)
  - Pass low_stock_threshold via extra_data in low_stock email send

customer-spa/src/pages/DynamicPage/sections/ImageTextSection.tsx

@@ -1,5 +1,6 @@
 import { cn } from '@/lib/utils';
 import { SharedContentLayout } from '@/components/SharedContentLayout';
+import { getSectionBackground } from '@/lib/sectionStyles';
 
 interface ImageTextSectionProps {
     id: string;
@@ -66,25 +67,40 @@ export function ImageTextSection({
     };
     const heightClasses = heightMap[heightPreset] || 'py-12 md:py-24';
 
+    const hasCustomBackground = !!styles?.backgroundColor || !!styles?.backgroundImage || styles?.backgroundType === 'gradient';
+    const sectionBg = getSectionBackground(styles);
+
+    // Helper to get background style for dynamic schemes
+    const getBackgroundStyle = (): React.CSSProperties | undefined => {
+        if (hasCustomBackground) return sectionBg.style;
+        if (colorScheme === 'primary') {
+            return { backgroundColor: 'var(--wn-primary, #1a1a1a)' };
+        }
+        if (colorScheme === 'secondary') {
+            return { backgroundColor: 'var(--wn-secondary, #6b7280)' };
+        }
+        return undefined;
+    };
+
     return (
         <section
             id={id}
             className={cn(
                 'wn-section wn-image-text',
                 `wn-scheme--${colorScheme}`,
-                heightClasses,
+                !styles?.paddingTop && !styles?.paddingBottom && heightClasses,
                 {
-                    'bg-muted': colorScheme === 'muted',
-                    'bg-primary/5': colorScheme === 'primary',
+                    'bg-muted': colorScheme === 'muted' && !hasCustomBackground,
                 }
             )}
+            style={getBackgroundStyle()}
         >
             <SharedContentLayout
                 title={title}
                 text={text}
                 image={image}
                 imagePosition={isImageRight ? 'right' : 'left'}
-                containerWidth={styles?.contentWidth === 'full' ? 'full' : 'contained'}
+                containerWidth={styles?.contentWidth === 'full' ? 'full' : styles?.contentWidth === 'boxed' ? 'boxed' : 'contained'}
                 titleStyle={titleStyle.style}
                 titleClassName={titleStyle.classNames}
                 textStyle={textStyle.style}