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/tests/evaluation/test_internal_router_auth.py

@@ -4,6 +4,7 @@ import pytest
 from httpx import ASGITransport, AsyncClient
 
 from app.features.evaluation.internal_auth import get_internal_eval_principal
+from tests.conftest import install_test_error_handlers
 
 
 @pytest.mark.asyncio
@@ -19,7 +20,7 @@ async def test_internal_eval_list_fixtures_requires_config(
     )
     from app.features.evaluation.router import router
 
-    app = FastAPI()
+    app = install_test_error_handlers(FastAPI())
     app.include_router(router, prefix="/internal/api/evaluation")
     transport = ASGITransport(app=app)
     async with AsyncClient(transport=transport, base_url="http://t") as client:
@@ -50,7 +51,7 @@ async def test_internal_eval_with_override_lists_fixtures(
 
     from app.features.evaluation.router import router
 
-    app = FastAPI()
+    app = install_test_error_handlers(FastAPI())
     app.include_router(router, prefix="/internal/api/evaluation")
 
     async def _override_auth():