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/core/logging.py

@@ -43,6 +43,7 @@ from app.core.log_events import (
     correlation_bind_kwargs,
     format_log_event,
 )
+from app.core.runtime_constants import agent_log_defaults
 
 if TYPE_CHECKING:
     from loguru import Logger
@@ -185,7 +186,7 @@ def _apply_third_party_log_levels() -> None:
     default_celery = logging.INFO if verbose else logging.WARNING
     default_httpx = logging.WARNING
 
-    raw_c = (settings.celery_log_level or "").strip()
+    raw_c = (agent_log_defaults.celery_log_level or "").strip()
     if raw_c:
         parsed = _parse_stdlib_level(raw_c)
         cel_level = parsed if parsed is not None else default_celery
@@ -195,7 +196,7 @@ def _apply_third_party_log_levels() -> None:
     for name in ("celery", "celery.worker"):
         logging.getLogger(name).setLevel(cel_level)
 
-    raw_h = (settings.httpx_log_level or "").strip()
+    raw_h = (agent_log_defaults.httpx_log_level or "").strip()
     if raw_h:
         parsed = _parse_stdlib_level(raw_h)
         httpx_level = parsed if parsed is not None else default_httpx
@@ -252,7 +253,7 @@ def setup_logging() -> None:
         diagnose=False,
     )
 
-    json_path = (settings.log_json_file or "").strip()
+    json_path = (agent_log_defaults.log_json_file or "").strip()
     if json_path:
         logger.add(
             json_path,