Clarify private prompt governance boundary

[chefmrfrizzle]

What changed

• document the governed private prompt lifecycle at a high level
• explicitly prohibit prompt registries, content locks, evaluator contracts, and execution tooling from the public repository
• record the private prompt safeguards in both plain language and technical terms

Why

The public repository should explain what is protected without exposing the protected machinery. This makes the separation easier to understand and harder to erode over time.

Security impact

No private prompt bodies, manifests, hashes, registry code, evaluator logic, credentials, client data, or production connectors are included. The public file manifest remains unchanged.

Verification

• npm test in the public repository
• private cross-repository boundary check against the public tree
• full private suite: 10 tests, deterministic verification, and prompt-content lock check

[11BUSD]

Owner review: approved. The change documents private prompt governance at a high level without publishing prompt bodies, registries, hashes, evaluator logic, execution tooling, credentials, or client data. Required verification and CodeQL checks pass.