Distills the design-language discussion on #3444 into a durable
reference: visual language, motion, theming policy, data-freshness/
refresh, error UX, empty states, layout/viewport, component-first
design, and attention — plus an open-questions table pointing at the
still-unbuilt issues (#3452/#3453/#3454/#3456) instead of asserting
them as settled.
Mirrors css-vars.md's shape and links to it + to /components rather
than duplicating either. First draft for comment, not a final spec.
