feat: Implement A4 invoice layout and hide Label for virtual orders

Invoice:
- Enhanced A4-ready layout with proper structure
- Store header with invoice number
- Billing/shipping address sections
- Styled items table with alternating rows
- Totals summary with conditional display
- Thank you footer

Label:
- Label button now hidden for virtual-only orders
- Uses existing isVirtualOnly detection

Print CSS:
- Added @page A4 size directive
- Print-color-adjust for background colors
- 20mm padding for proper margins

Documentation:
- Updated subscription module plan (comprehensive)
- Updated affiliate module plan (comprehensive)
- Created shipping label standardization plan

admin-spa/src/index.css

@@ -34,6 +34,7 @@
     --chart-5: 27 87% 67%;
     --radius: 0.5rem;
   }
+
   .dark {
     --background: 222.2 84% 4.9%;
     --foreground: 210 40% 98%;
@@ -63,10 +64,23 @@
 }
 
 @layer base {
-  * { @apply border-border; }
-  body { @apply bg-background text-foreground; }
-  h1, h2, h3, h4, h5, h6 { @apply text-foreground; }
-  
+  * {
+    @apply border-border;
+  }
+
+  body {
+    @apply bg-background text-foreground;
+  }
+
+  h1,
+  h2,
+  h3,
+  h4,
+  h5,
+  h6 {
+    @apply text-foreground;
+  }
+
   /* Override WordPress common.css focus/active styles */
   a:focus,
   a:active {
@@ -126,11 +140,14 @@
 
 /* Page defaults for print */
 @page {
-  size: auto;              /* let the browser choose */
-  margin: 12mm;            /* comfortable default */
+  size: auto;
+  /* let the browser choose */
+  margin: 12mm;
+  /* comfortable default */
 }
 
 @media print {
+
   /* Hide WordPress admin chrome */
   #adminmenuback,
   #adminmenuwrap,
@@ -139,44 +156,124 @@
   #wpfooter,
   #screen-meta,
   .notice,
-  .update-nag { display: none !important; }
+  .update-nag {
+    display: none !important;
+  }
 
   /* Reset layout to full-bleed for our app */
-  html, body, #wpwrap, #wpcontent { background: #fff !important; margin: 0 !important; padding: 0 !important; }
-  #woonoow-admin-app, #woonoow-admin-app > div { margin: 0 !important; padding: 0 !important; max-width: 100% !important; }
+  html,
+  body,
+  #wpwrap,
+  #wpcontent {
+    background: #fff !important;
+    margin: 0 !important;
+    padding: 0 !important;
+  }
+
+  #woonoow-admin-app,
+  #woonoow-admin-app>div {
+    margin: 0 !important;
+    padding: 0 !important;
+    max-width: 100% !important;
+  }
 
   /* Hide elements flagged as no-print, reveal print-only */
-  .no-print { display: none !important; }
-  .print-only { display: block !important; }
+  .no-print {
+    display: none !important;
+  }
+
+  .print-only {
+    display: block !important;
+  }
 
   /* Improve table row density on paper */
-  .print-tight tr > * { padding-top: 6px !important; padding-bottom: 6px !important; }
+  .print-tight tr>* {
+    padding-top: 6px !important;
+    padding-bottom: 6px !important;
+  }
 }
 
 /* By default, label-only content stays hidden unless in print or label mode */
-.print-only { display: none; }
+.print-only {
+  display: none;
+}
 
 /* Label mode toggled by router (?mode=label) */
-.woonoow-label-mode .print-only { display: block; }
+.woonoow-label-mode .print-only {
+  display: block;
+}
+
 .woonoow-label-mode .no-print-label,
 .woonoow-label-mode .wp-header-end,
-.woonoow-label-mode .wrap { display: none !important; }
+.woonoow-label-mode .wrap {
+  display: none !important;
+}
 
 /* Optional page presets (opt-in by adding the class to a wrapper before printing) */
-.print-a4 { }
-.print-letter { }
-.print-4x6 { }
+.print-a4 {}
+
+.print-letter {}
+
+.print-4x6 {}
+
 @media print {
-  .print-a4 { }
-  .print-letter { }
+
+  /* A4 Invoice layout */
+  @page {
+    size: A4;
+    margin: 0;
+  }
+
+  .print-a4 {
+    width: 210mm !important;
+    min-height: 297mm !important;
+    padding: 20mm !important;
+    margin: 0 auto !important;
+    box-sizing: border-box !important;
+    background: white !important;
+    -webkit-print-color-adjust: exact !important;
+    print-color-adjust: exact !important;
+  }
+
+  .print-a4 * {
+    -webkit-print-color-adjust: exact !important;
+    print-color-adjust: exact !important;
+  }
+
+  /* Ensure backgrounds print */
+  .print-a4 .bg-gray-50 {
+    background-color: #f9fafb !important;
+  }
+
+  .print-a4 .bg-gray-900 {
+    background-color: #111827 !important;
+  }
+
+  .print-a4 .text-white {
+    color: white !important;
+  }
+
+  .print-letter {}
+
   /* Thermal label (4x6in) with minimal margins */
-  .print-4x6 { width: 6in; }
-  .print-4x6 * { -webkit-print-color-adjust: exact; print-color-adjust: exact; }
+  .print-4x6 {
+    width: 6in;
+  }
+
+  .print-4x6 * {
+    -webkit-print-color-adjust: exact;
+    print-color-adjust: exact;
+  }
 }
 
 /* --- WooNooW: Popper menus & fullscreen fixes --- */
-[data-radix-popper-content-wrapper] { z-index: 2147483647 !important; }
-body.woonoow-fullscreen .woonoow-app { overflow: visible; }
+[data-radix-popper-content-wrapper] {
+  z-index: 2147483647 !important;
+}
+
+body.woonoow-fullscreen .woonoow-app {
+  overflow: visible;
+}
 
 /* --- WooCommerce Admin Notices --- */
 .woocommerce-message,