Update README with usage instructions (litmus-9uzr)
README update with usage instructions for the final MVP.
Summary of Changes
Rewrote README to reflect the implemented MVP:
- Feature list covering 19 themes, 5 scenes, contrast validation, comparison, dual navigation
- Getting started section with CLI and web app run commands
- Project structure overview with key modules
- Architecture explanation: semantic color refs, provider/consumer model
- Trimmed speculative design sections, kept concise future directions