Milestone 8: documentation reconciliation and clean-user testing

[anthfuller]

Summary

• reconcile supported commands with actual clean-environment behavior
• add an isolated clean-user acceptance gate and documentation invariants
• classify the broken non-canonical OPA walkthrough as illustrative and unsupported
• remove the placeholder test and two empty placeholder walkthroughs

Reviewed scope

• Base: 5f42f6dfe4d108f310061b72b848a9db85d60659
• Head: 2503b2671dbd280d4c180aecf53382019c506362
• Tree: f04a3849e7a5389b5862a8e023a9854bd9a12444
• 2 commits; 17 files; 442 additions; 150 deletions

Validation

• isolated hash-locked installation on Python 3.12.14
• checksum-verified OPA 1.20.2
• 96 tests passed
• canonical execution, evidence verification, and deterministic replay passed
• golden structural evaluation passed: 4 scenarios, 1.00 success rate
• dependency audit found no known vulnerabilities
• documentation links, fences, command boundaries, Gitleaks, whitespace, and whitepaper integrity passed

Independent review approved this exact head for PR creation. Do not merge until PR-head GitHub Actions and final review pass.