feature: Next.js Shopify e-commerce template

[emwp]

Add Next.js Shopify E-commerce Template

Description

This PR adds a new nextjs/shopify-ecommerce template that demonstrates building a production-ready e-commerce application using Next.js 14+ and Shopify's Storefront API. The template follows the same deployment patterns as our basic Next.js starter (referenced in starters/nextjs/basic) while adding e-commerce specific features and Shopify integration.

Key Features

• App Router implementation with React Server Components
• Dynamic product catalog with ISR for optimal performance
• Shopping cart using Shopify's Cart API
• Customer authentication via Shopify Customer Accounts
• Checkout process using Shopify Checkout (Hosted checkout page using Stripe under the hood)
• Shopify inventory management
• Responsive design with Tailwind CSS
• TypeScript implementation

Firebase Services Utilized

• App Hosting for deployment
• Firebase Data Connect for customer reviews

Technical Implementation

The template maintains compatibility with Firebase App Hosting's configuration-free deployment process and follows the same structure as our basic Next.js starter:

• Implements SSR/ISR/SSG patterns demonstrated in the basic starter
• Follows the established project structure and coding standards

Testing

• ✅ Verified e-commerce flows locally
• ✅ Tested deployment to Firebase App Hosting
• ✅ Validated Shopify integration
• ✅ Tested with the two latest LTS Node.js versions (20, 22)

Documentation

Added documentation covering:

• Template setup and configuration
• Shopify integration steps
• Environment variables
• Deployment process
• Local development workflow