release: final assurance closure and experimental 0.x readiness

[fraware]

Final release-candidate closure. No new product features.

This PR closes the final audit findings before an experimental 0.x tag:

• preserves fixture-substitution rejection while correcting obsolete unsupported-mode tests;
• makes production-generated Lean execution a required gate for every CR-eligible exact capability, including all four exact-enabled linear-algebra operations;
• separates offline bundle replay maturity from offline kernel theorem replay maturity;
• corrects maturity-inventory provenance semantics;
• aligns current status/CI messaging with live assurance semantics;
• strengthens release provenance and release-facing documentation in subsequent closure commits.

Non-negotiable: no checker/audit weakening and no promotion based on fixture replay, benchmark success, or structural source generation alone. Stable promotion and human/external governance gates remain separate and are not being fabricated here.