docs: clarify eval policy quickstart

[aryeko]

Motivation

Phase 1 clarifies the global eval policy for eval-kit consumers so CI remains fast, offline, and structural while deterministic semantic suites stay local on-demand and Promptfoo/Codex model-assisted evals remain manual/advisory.

Scoped changes

• Document the three eval lanes across quickstart, integration, reference, design, examples, and skills docs.
• Update consumer shell examples to use pnpm exec eval-kit while keeping package scripts on plain eval-kit.
• State that run-producing/model-assisted evals are not default CI gates.
• Keep the bootstrap doctor contract accurate by separating suite validation checks from CI policy guidance.

Verification

• pnpm format
• pnpm check
• git diff --check

Approved local commit: 75c027ec4787c185c32f5738fe3e957703b4c1b4.