docs: 5-minute verify.py example against metis.modelmarket.dev

[alexar76]

Why

Metis is pin-worthy only if a newcomer can verify something today without reading the whole cognition stack.

Task

Add examples/verify_live.py (or expand README Quick Start) that:

1. POSTs a short prompt to the public Metis verify endpoint (https://metis.modelmarket.dev — use the same path the HTTP client already uses)
2. Prints verify_score / verified / truncated answer
3. Documents required env vars (none for public demo if possible; otherwise AIMARKET_METIS_KEY)

Acceptance

• python examples/verify_live.py works against prod (or clearly documents when it needs a key)
• Linked from README under Quick Start
• ≤40 lines of code