feat: add E-Commerce Engineer agent

[itlasso]

What does this PR do?

Adds a new E-Commerce Engineer agent to the Engineering Division, specializing in Shopify, WooCommerce, and Drupal Commerce storefront development, custom checkout flows, and payment gateway integration.

Agent Information (if adding/modifying an agent)

• Agent Name: E-Commerce Engineer
• Category: Engineering
• Specialty: Shopify Liquid theme development, WooCommerce custom product types and checkout, Drupal Commerce order processors and payment gateways, Stripe/PayPal/Klarna integration, product catalog architecture, and e-commerce performance optimization

Checklist

• Follows the agent template structure from CONTRIBUTING.md
• Includes YAML frontmatter with name, description, color
• Has concrete code/template examples (for new agents)
• Tested in real scenarios
• Proofread and formatted correctly