rewrite README: concise, honest, link to docs

- Add motivation section (view=f(state), no binding)
- Add "Who Is This For?" with honest pros/cons
- Group features by category
- Simplify quick start example
- Add dependencies and documentation tables
- Remove architecture details (link to ARCHITECTURE.md)
- Remove event handling, layout system, best practices sections
- 167 lines vs ~400 before

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mike-ward