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.lf

@@ -0,0 +1,11 @@
+# Shopify Store Configuration
+SHOPIFY_SHOP_DOMAIN=starlit-night-test-store.myshopify.com
+SHOPIFY_ACCESS_TOKEN=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
+
+# Price Update Configuration
+TARGET_TAG=summer-sale
+
+# Optional Configuration
+# PRICE_ADJUSTMENT_PERCENTAGE can be positive (increase) or negative (decrease)
+# Example: 10 = 10% increase, -15 = 15% decrease
+PRICE_ADJUSTMENT_PERCENTAGE=-10