Expand design.md to cover the whole system

Document both token vocabularies (app shadcn names and the marketing
--color-* mirror) with a mapping table, the sources of truth and font-loading
points, the mono-metadata system, every signature pattern (frame guides,
graph-paper texture, connection diagram, mono index numerals, trace
waterfall), the real app and marketing component vocabularies, the marks
policy (favicons for the app, brand SVGs for marketing), and the
status-via-grayscale rule. Records the marketing illustration color exceptions
(code syntax tokens, connection-matrix status dots) honestly.

Author: RhysSullivan