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/adapters/image_gen/liblib_provider.py

@@ -16,6 +16,8 @@ import httpx
 
 from app.core.config import settings
 from app.core.logging import get_logger
+from app.features.memoir.constants import memoir
+from app.core.runtime_constants import misc_defaults
 
 logger = get_logger(__name__)
 
@@ -62,7 +64,7 @@ class LiblibImageProvider:
         self.access_key = access_key or (settings.liblib_access_key or "")
         self.secret_key = secret_key or (settings.liblib_secret_key or "")
         self.base_url = (
-            base_url or settings.liblib_base_url or "https://openapi.liblibai.cloud"
+            base_url or misc_defaults.liblib_base_url or "https://openapi.liblibai.cloud"
         ).rstrip("/")
         self.template_uuid = template_uuid or (
             settings.liblib_template_uuid or DEFAULT_LIBLIB_TEMPLATE_UUID
@@ -240,7 +242,7 @@ def _build_allowed_download_hosts(
     if configured_hosts is None:
         configured_hosts = tuple(
             host.strip().lower()
-            for host in (settings.memoir_image_download_hosts or "").split(",")
+            for host in (memoir.image_download_hosts or "").split(",")
             if host.strip()
         )
     base_hostname = (urlparse(base_url).hostname or "").lower()