chore(openspec): archive engineering-docs and phase-2-production-ready changes

- engineering-docs → archive/2026-03-29-engineering-docs (63/63 tasks complete)
- phase-2-production-ready → archive/2026-03-29-phase-2-production-ready (89/89 tasks complete)
- openspec/specs/ synced with all Phase 1 + Phase 2 + engineering-docs capabilities (22 specs total)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openspec/specs/vault/spec.md

@@ -0,0 +1,21 @@
+# Spec: HashiCorp Vault Integration
+
+**Status**: Pending CEO approval
+**Workstream**: 1 of 8
+
+## Scope
+- VaultClient class wrapping `node-vault`
+- `005_add_vault_path.sql` migration
+- Updated CredentialService to write secrets to Vault instead of PostgreSQL
+- New env vars: VAULT_ADDR, VAULT_TOKEN, VAULT_MOUNT
+- Migration guide: bcrypt → Vault coexistence strategy
+
+## Acceptance Criteria
+- [ ] New credentials: secret written to Vault KV v2, `vault_path` stored in PostgreSQL
+- [ ] Credential rotation: Vault versioned update, `vault_path` unchanged
+- [ ] Credential revocation: Vault secret deleted, DB status = `revoked`
+- [ ] Existing bcrypt credentials continue to work until rotated
+- [ ] VaultClient follows existing service interface pattern (DRY, SOLID)
+- [ ] Zero `any` types, TypeScript strict
+- [ ] `VAULT_ADDR` / `VAULT_TOKEN` validation at startup (fail-fast)
+- [ ] DevOps docs updated with Vault setup section