feat(data-safety): scheduled DB backups + audit trail + verified actor attribution

- db-backup sidecar: pg_dump -Fc of procurement+casdoor every
  BACKUP_INTERVAL_SECONDS into BACKUP_DIR, retention via BACKUP_KEEP_DAYS
- audit_log table (migration.sql + runtime ensure_audit_table) with
  model + transactional helper (utils/audit.record) — wired into user
  create/role-change and inventory transaction creation
- get_actor: quote_events.actor now stores the VERIFIED user's display
  name instead of the raw bearer token

.env.example

@@ -40,6 +40,11 @@ DEV_LOGIN_ENABLED=false
 # --- Deploy webhook (Gitea push → rebuild; see infra/deploy-webhook/) ---
 GITEA_WEBHOOK_SECRET=CHANGE_ME_long_random_webhook_secret
 
+# --- Backups (db-backup sidecar; see docker-compose.yml) ---
+BACKUP_DIR=/srv/erp/backups
+BACKUP_INTERVAL_SECONDS=86400
+BACKUP_KEEP_DAYS=14
+
 # --- Monitoring stack (see monitoring/README.md) ---
 # API log format for Loki ingestion ("text" locally, "json" in production)
 LOG_FORMAT=json