White Mountaineering Style Design System (DESIGN.md, Japanese UI)

Design policy: A monochrome, hard-edged fashion EC. Composed only of black, white, and gray, it makes the product photos and the mountain-line logo stand out - Density: Medium to low density. The hero is a full-screen visual, while the nav and product grid are orderly and evenly spaced - Keywords: Monochrome / hard-edged / grid / minimal / mode - Shape language: No rounded corners whatsoever (border-radius: 0). Buttons, inputs, and cards are all right-angled. Areas are divided by thin rules - Typeface character: Helvetica is placed in the leading role, and the Latin characters in the nav, butt