feat: integrate design tokens from www.makepostsell.com styleguide

• Add tokens.css as foundation layer (loaded before common.css)
  • Color system: brand, surface, text, border, state, alert tokens
  • Typography: major third scale with 14 semantic classes
  • Spacing: 4px base, 12-step scale with utility classes
  • Shape: 7 radius levels from none to pill
  • Elevation: 5 shadow levels with dual-shadow technique
  • Motion: 4 easing curves, 7 durations, entrance animations
  • Loading: skeleton shimmer + spinner (3 sizes)
  • Scroll reveal, state layers, ripple effect, focus rings
  • Accessibility: prefers-reduced-motion, :focus-visible
• Rewrite styleguide.j2 to comprehensive design system reference
  • New sections: tokens, elevation, motion, spacing, shape, states, loading, status notices, cart buttons, checkout layout, toggle
  • All app components documented with live demos
  • TOC navigation for all sections
• Add STYLEGUIDE rule to CLAUDE.md
• Wire tokens.css into base.j2 before common.css

Exploration branch — tokens.css provides new variables alongside existing common.css variables. No visual regressions expected as common.css values take precedence for shared property names.

Summary by CodeRabbit

• New Features

  • Gift cards: purchase, apply discounts at checkout, check balance, and manage inventory
  • Bring Your Own Bucket (BYOB): shops can configure custom S3 storage for media uploads
  • Shop environments: production, staging, and development designation options
  • 21-day free trial for newly created shops
  • Enhanced design system with tokens, components, and typography utilities

• Improvements

  • Updated media delivery to use shop-specific CDN endpoints
  • Enhanced cart with gift card discount support alongside coupons
  • Discovery search respects shop environment settings

• Documentation

  • Added comprehensive design system documentation
  • Updated architecture reference with new features
  • Enhanced development guidelines and test coverage requirements