Add Puck storefront page editor

[AJFrio]

Summary

• add Puck-backed page content storage and validation for Home/About pages
• replace the old page-content settings panels with a lazy-loaded Puck Pages tab
• render Puck JSON on the public Home/About storefront pages while keeping products, collections, nav, footer, cart, and checkout code-owned
• document the new APIs/KV model and cover service/public/admin route behavior with tests

Local validation

• npm run harness:validate passed
• npm test -- --run passed
• npm run build passed
• npm run lint currently fails on pre-existing unrelated unused-variable/hook warnings outside this change; changed-file ESLint passed before commit