CAINZ Style Design System (DESIGN.md, Japanese UI)

Design policy: Establishes a deep forest green #006438 as the brand color and builds a practical, clean EC layout. The orange #e86e0c search button serves as an accent that guides the eye, while the sale red #b81a35 handles price appeal. Characterized by pill-shaped tag navigation and a Tailwind/MUI hybrid implementation - Density: EC-style with product cards densely arranged in a grid. Body text 14px / line-height 1.5, a standard density for Japanese EC. Compresses and displays many categories via the scroll navigation of tag pills - Keywords: Forest green, practical EC, pill tag navigation,