runtime-v0.4.42: REUSE-REGISTRY-GUARD

Baked-asset registry + reuse-before-rewrite guard. New asset_registry verb-support module (count stays 20) + register-asset / reuse-check CLI verbs + drift_audit.check_asset_registry auditor. Lean-RAG storage: inventory in the non-loaded RAG_CONTEXT.json baked_assets partition; concise reuse_registry_guard pointer in MASTER. Closes the anti-redundancy gap where agents re-author already-baked artifacts (eBay S12 field evidence + S165/E-069 design-level instance). health 21/21, drift gate 268149294421 unchanged, suite 1946 -> 1964 green (+18).