Implement AUDIT-WP-0007 hash-chain integrity.

Accept now extends a single-schema chain. Verify walks it; a rewritten
payload_hash is a break. Tamper evidence is that detector plus an
external chain-head attestation, not WORM.

deploy/audit-core.yaml

@@ -46,11 +46,11 @@ metadata:
     # Rollback position. Update both together; `kubectl rollout undo` returns to
     # the previous digest, and the schema note records whether that is safe.
     audit-core.railiance.io/rollback-note: >-
-      Migrations 0001-0005 are additive (CREATE TABLE/INDEX/TRIGGER IF NOT
-      EXISTS, plus GRANTs) and are not reversed by a rollback. An older image
-      runs against the newer schema without harm. A future migration that drops
-      or narrows a column breaks that property and must state its own rollback
-      position before it is released.
+      Migrations 0001-0006 are additive. 0006 adds chain_hash/chain_prev and
+      then NOT NULL. An image that does not write those columns cannot accept
+      events after 0006. Do not roll back past sha256:05fe1c06… to a pre-0007
+      writer. A future migration that drops or narrows a column must state
+      its own rollback position before it is released.
 spec:
   replicas: 1
   revisionHistoryLimit: 5