Add trading module section (§13) to architecture.md covering commands, data model, price sources, and file layout. Update file trees, test counts (56→110), and module registry snippet in both docs.
- README: add "Why" value prop, request-flow ASCII diagram, and "Further reading" links to the docs directory - docs/architecture.md: new 14-section guide covering cold-start flow, module contract, static loader rationale, unified-namespace conflict detection, dispatcher minimalism, KVStore prefixing mechanics, deploy flow, security posture, testing philosophy, and non-goals
