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

Design policy: Four brand colors (Blue / Red / Orange / Green) are placed on a white background as signals for functional categories. Text is unified in a calm dark gray of #333333, producing the sense of trust and cleanliness expected of a news media brand - Density: Body line-height is a generous 1.8. Headings are set tightly (-0.025em) to create an information hierarchy. Mobile-first, adopting fluid typography via text-dynamic-min-* - Keywords: News blue, four-color category badges, the system-native feel of system-ui, flat and clean white base, mobile-first - Characteristics: - The consume