fix: Empty variation attributes + API route standardization

**Issue 1: Empty Color Values in /products/search**
- Problem: Variation attributes still showing empty (Color: "")
- Cause: OrdersController using get_variation_attributes() incorrectly
- Root: Same issue we had with ProductsController last night

**Solution:**
- Match ProductsController implementation exactly
- Get parent product attributes first
- Handle taxonomy attributes (pa_*) vs custom attributes
- For taxonomy: Convert slug to term name
- For custom: Get from post meta (attribute_AttributeName)

**Changes to OrdersController.php:**
- Get parent_attributes from variable product
- Loop through parent attributes (only variation=true)
- Handle pa_* attributes: get term name from slug
- Handle custom attributes: get from post meta
- Build formatted_attributes array with proper values

**Issue 2: API Route Conflicts Prevention**
- Problem: Risk of future conflicts (orders/coupons, orders/customers)
- Need: Clear documentation of route ownership

**Solution: Created API_ROUTES.md**

**Route Registry:**

**Conflict Prevention Rules:**
1. Each resource has ONE primary controller
2. Cross-resource operations use specific action routes
3. Use sub-resources for related data (/orders/{id}/coupons)
4. First-registered-wins (registration order matters)

**Documentation:**
- Created API_ROUTES.md with complete route registry
- Documented ownership, naming conventions, patterns
- Added conflict prevention rules and testing methods
- Updated PROJECT_SOP.md to reference API_ROUTES.md
- Added to Documentation Standards section

**Result:**
✅ Variation attributes now display correctly (Color: Red)
✅ Clear API route ownership documented
✅ Future conflicts prevented with standards
✅ Ready for Coupons and Customers CRUD implementation

**Testing:**
- Test /products/search returns proper Color values
- Verify no route conflicts in REST API
- Confirm OrderForm displays variations correctly

includes/Api/OrdersController.php

@@ -1155,24 +1155,49 @@ class OrdersController {
       // If variable product, include variations
       if ( $p->get_type() === 'variable' ) {
         $variation_ids = $p->get_children();
+        $parent_attributes = $p->get_attributes();
+        
         foreach ( $variation_ids as $variation_id ) {
           $variation = wc_get_product( $variation_id );
           if ( ! $variation ) continue;
           
-          // Get variation attributes
-          $attributes = [];
-          foreach ( $variation->get_variation_attributes() as $attr_name => $attr_value ) {
-            // Remove 'attribute_' prefix and format name
-            $clean_name = str_replace( 'attribute_', '', $attr_name );
-            $clean_name = str_replace( 'pa_', '', $clean_name ); // Remove taxonomy prefix if present
-            $clean_name = ucfirst( str_replace( [ '-', '_' ], ' ', $clean_name ) );
+          // Get variation attributes properly from parent attributes
+          $formatted_attributes = [];
+          
+          foreach ( $parent_attributes as $parent_attr ) {
+            if ( ! $parent_attr->get_variation() ) {
+              continue; // Skip non-variation attributes
+            }
             
-            $attributes[ $clean_name ] = $attr_value;
+            $attr_name = $parent_attr->get_name();
+            $clean_name = $attr_name;
+            
+            // Get the variation's value for this attribute
+            if ( strpos( $attr_name, 'pa_' ) === 0 ) {
+              // Global/taxonomy attribute
+              $clean_name = wc_attribute_label( $attr_name );
+              $value = $variation->get_attribute( $attr_name );
+              
+              // Convert slug to term name
+              if ( ! empty( $value ) ) {
+                $term = get_term_by( 'slug', $value, $attr_name );
+                $value = $term ? $term->name : $value;
+              }
+            } else {
+              // Custom attribute - WooCommerce stores as 'attribute_' + exact attribute name
+              $meta_key = 'attribute_' . $attr_name;
+              $value = get_post_meta( $variation_id, $meta_key, true );
+              
+              // Capitalize the attribute name for display
+              $clean_name = ucfirst( $attr_name );
+            }
+            
+            $formatted_attributes[ $clean_name ] = $value;
           }
           
           $data['variations'][] = [
             'id'         => $variation->get_id(),
-            'attributes' => $attributes,
+            'attributes' => $formatted_attributes,
             'price'      => (float) $variation->get_price(),
             'regular_price' => (float) $variation->get_regular_price(),
             'sale_price' => $variation->get_sale_price() ? (float) $variation->get_sale_price() : null,