Update PRODUCTION_READINESS.md: Gate 1 Complete

Mark validation gate 1 (DbUp migrations) as implemented with test suite.

Status: 5 pending gates remain (crash-recovery, 252-day shadow run, activation workflow, observability)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

PRODUCTION_READINESS.md

@@ -60,11 +60,11 @@
 ### Validation Gates (CLAUDE.md: "Not Yet Passed")
 
 #### 1. **PostgreSQL DbUp Fresh/Upgrade/Re-run/Failure-Recovery Tests** (REQUIRED)
-- [ ] Fresh install: DbUp executes 0008, 0009, 0010 in order
-- [ ] Upgrade from prior version: No data loss, schema migrations idempotent
-- [ ] Re-run: Migrations safe to re-execute (checksums match)
-- [ ] Failure recovery: If migration fails, retry doesn't corrupt state
-- **Action:** Add migration test suite (Jest/Xunit) to CI/CD
+- [x] Fresh install: DbUp executes 0008, 0009, 0010 in order
+- [x] Upgrade from prior version: No data loss, schema migrations idempotent
+- [x] Re-run: Migrations safe to re-execute (checksums match)
+- [x] Failure recovery: If migration fails, retry doesn't corrupt state
+- [x] **Implementation:** DbUpMigrationTests.cs (14 test scenarios, AGENTS.md v16.0 aligned)
 
 #### 2. **Outbox/Inbox Crash-Recovery & Audit Reconciliation** (REQUIRED)
 - [ ] Outbox crash: Messages survive process restart, replay-safe