refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/scripts/verify_observability_metrics.sh

@@ -34,7 +34,7 @@ done
 
 if [[ "${fail}" -ne 0 ]]; then
   echo ""
-  echo "Some metrics missing. Ensure OTEL_ENABLED=true, API/worker running, and traffic generated."
+  echo "Some metrics missing. Ensure config deploy.otel_enabled=true, observability compose running, API/worker up, and traffic generated."
   exit 1
 fi
 echo "All required metrics present."