feat: Update Orders to follow CRUD pattern SOP

Following PROJECT_SOP.md section 5.7 CRUD Module Pattern:

**Backend (NavigationRegistry.php):**
- Added Orders submenu: All orders | New
- Prepared for future tabs (Drafts, Recurring)

**Frontend (Orders/index.tsx):**
- Removed 'New order' button from toolbar
- Kept bulk actions (Delete) in toolbar
- Filters remain in toolbar

**Result:**
- Orders now consistent with Products pattern
- Follows industry standard (Shopify, WooCommerce)
- Submenu for main actions, toolbar for filters/bulk actions

**Next:**
- Implement variable product handling in OrderForm

includes/Compat/NavigationRegistry.php

@@ -117,7 +117,11 @@ class NavigationRegistry {
                 'label'    => __('Orders', 'woonoow'),
                 'path'     => '/orders',
                 'icon'     => 'receipt-text',
-                'children' => [], // Orders has no submenu by design
+                'children' => [
+                    ['label' => __('All orders', 'woonoow'), 'mode' => 'spa', 'path' => '/orders'],
+                    ['label' => __('New', 'woonoow'), 'mode' => 'spa', 'path' => '/orders/new'],
+                    // Future: Drafts, Recurring, etc.
+                ],
             ],
             [
                 'key'      => 'products',