docs: explain real-world impact up front

[aantenore]

What changed

• opens the README with a plain-language problem, audience, solution, and concrete generic-change example
• maps the main architecture features to benefits a non-specialist can understand
• states alpha maturity, signature, certification, and intent-understanding limits up front

Why

Readers can understand the real-world value before entering the contract and conformance details.

Validation

• npm run check
• 92 tests passed
• repository identity and history audit passed