feat: implement XML validation for Google Shopping schema compliance and add validation script

prerender.cjs

@@ -699,6 +699,26 @@ const renderApp = async (categoryData, socket) => {
         console.log(`   - File verification: ⚠️ ${verifyError.message}`);
       }
       
+      // Validate XML against Google Shopping schema
+      try {
+        const ProductsXmlValidator = require('./scripts/validate-products-xml.cjs');
+        const validator = new ProductsXmlValidator(productsXmlPath);
+        const validationResults = await validator.validate();
+        
+        if (validationResults.valid) {
+          console.log(`   - Schema validation: ✅ Valid Google Shopping RSS 2.0`);
+        } else {
+          console.log(`   - Schema validation: ⚠️ ${validationResults.summary.errorCount} errors, ${validationResults.summary.warningCount} warnings`);
+          
+          // Show first few errors for quick debugging
+          if (validationResults.errors.length > 0) {
+            console.log(`   - First error: ${validationResults.errors[0].message}`);
+          }
+        }
+      } catch (validationError) {
+        console.log(`   - Schema validation: ⚠️ Validation failed: ${validationError.message}`);
+      }
+      
     } catch (error) {
       console.error(`❌ Error generating products.xml: ${error.message}`);
       console.log("\n⚠️  Skipping products.xml generation due to errors");