Adds a CSS-first responsive foundation with breakpoint tokens, fluid
typography/spacing via clamp(), and matchMedia-driven hooks. Portal
chrome swaps to an off-canvas drawer below md; workspace (IDE) shows
a friendly mobile gate below md with links to portal routes.
Details in docs/ux-responsive-strategy.md.
Co-Authored-By: Nakamoto, S <defi@defi-oracle.io>