Remove stale prototype framing

[stacknil]

Summary

• replace stale README MVP/prototype wording with local reviewer-oriented detection workflow lab framing
• clarify reviewer brief limitations as small-scope detection workflow demos
• add reviewer-doc assertions to prevent stale prototype/MVP wording from returning

Validation

• pytest tests/test_reviewer_docs.py --basetemp .pytest-artifacts-stale-framing
• pytest --basetemp .pytest-artifacts-full-stale-framing
• git diff --check
• git diff privacy/secret keyword scan