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/memoir/deps.py

@@ -1,18 +1,17 @@
 """Memoir feature dependencies: get_memoir_service（注入 MemoryService 供章节生成使用 evidence）。"""
 
 from fastapi import Depends
-from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.core.db import get_async_db
 from app.core.dependencies import get_object_storage
 from app.features.memoir.service import MemoirService
 from app.features.memory.deps import get_memory_service
 from app.features.memory.service import MemoryService
 from app.ports.storage import ObjectStorage
+from app.core.deps_types import DbDep
 
 
 def get_memoir_service(
-    db: AsyncSession = Depends(get_async_db),
+    db: DbDep,
     memory_service: MemoryService = Depends(get_memory_service),
     object_storage: ObjectStorage = Depends(get_object_storage),
 ) -> MemoirService: