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/cos_url_keys.py

@@ -8,6 +8,7 @@ from urllib.parse import urlparse
 from app.core.config import settings
 from app.core.logging import get_logger
 from app.ports.storage import ObjectStorage
+from app.core.runtime_constants import misc_defaults
 
 logger = get_logger(__name__)
 
@@ -35,7 +36,7 @@ def extract_cos_object_key_if_owned(url: str | None) -> str | None:
 
     candidates: list[str] = []
     bucket = (settings.tencent_cos_bucket or "").strip().lower()
-    region = (settings.tencent_cos_region or "").strip().lower()
+    region = (misc_defaults.tencent_cos_region or "").strip().lower()
     if bucket and region:
         candidates.append(f"{bucket}.cos.{region}.myqcloud.com")
     base = (settings.tencent_cos_base_url or "").strip()
@@ -135,7 +136,7 @@ def avatar_url_for_api_response(stored_url: str | None) -> str | None:
     if not key:
         return s
     if not (
-        (settings.tencent_cos_secret_id or "").strip()
+        (settings.tencent_secret_id or "").strip()
         and (settings.tencent_cos_bucket or "").strip()
     ):
         return s
@@ -159,7 +160,7 @@ def best_effort_delete_cos_object_for_url(url: str | None) -> None:
     if not key:
         return
     if not (
-        (settings.tencent_cos_secret_id or "").strip()
+        (settings.tencent_secret_id or "").strip()
         and (settings.tencent_cos_bucket or "").strip()
     ):
         return