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/app/features/evaluation/internal_auth.py

@@ -2,9 +2,10 @@
 
 from typing import Annotated
 
-from fastapi import Depends, Header, HTTPException, status
+from fastapi import Depends, Header
 
 from app.core.config import settings
+from app.core.errors import AuthenticationError, ServiceUnavailableError
 from app.core.logging import get_logger
 
 logger = get_logger(__name__)
@@ -22,9 +23,8 @@ class InternalEvalPrincipal:
 def require_internal_eval_enabled() -> None:
     if not (settings.internal_eval_api_key or "").strip():
         logger.warning("internal_eval_api_key 未配置，内部评测 API 拒绝访问")
-        raise HTTPException(
-            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
-            detail="内部评测服务未启用（缺少 INTERNAL_EVAL_API_KEY）",
+        raise ServiceUnavailableError(
+            "内部评测服务未启用（缺少 INTERNAL_EVAL_API_KEY）"
         )
 
 
@@ -37,16 +37,10 @@ def verify_internal_eval_key(
     require_internal_eval_enabled()
     expected = (settings.internal_eval_api_key or "").strip()
     if not expected:
-        raise HTTPException(
-            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
-            detail="内部评测服务未启用",
-        )
+        raise ServiceUnavailableError("内部评测服务未启用")
     provided = (header_value or query_value or "").strip()
     if not provided or provided != expected:
-        raise HTTPException(
-            status_code=status.HTTP_401_UNAUTHORIZED,
-            detail="无效的内部评测密钥",
-        )
+        raise AuthenticationError("无效的内部评测密钥")
     return InternalEvalPrincipal()