Initial commit: Complete Shopify Price Updater implementation

- Full Node.js application with Shopify GraphQL API integration
- Compare At price support for promotional pricing
- Comprehensive error handling and retry logic
- Progress tracking with markdown logging
- Complete test suite with unit and integration tests
- Production-ready with proper exit codes and signal handling

.env.example

@@ -0,0 +1,11 @@
+# Shopify Store Configuration
+SHOPIFY_SHOP_DOMAIN=your-shop-name.myshopify.com
+SHOPIFY_ACCESS_TOKEN=your-admin-api-access-token
+
+# Price Update Configuration
+TARGET_TAG=sale
+PRICE_ADJUSTMENT_PERCENTAGE=10
+
+# Optional Configuration
+# PRICE_ADJUSTMENT_PERCENTAGE can be positive (increase) or negative (decrease)
+# Example: 10 = 10% increase, -15 = 15% decrease