refactor(cache): 統一 cache SOT 並啟用 gunicorn preload

ADR-017 Phase 3f-2：新增 services/cache_manager.py，讓 sales/import/export/daily/dashboard 共用同一份 in-memory cache；cache_service 改為相容 shim；Dockerfile/docker-compose 啟用 gunicorn --preload。

docker-compose.yml

@@ -48,7 +48,7 @@ services:
     ports:
       - "127.0.0.1:5003:80"  # 僅本地連線，透過 Nginx 反向代理（nginx 反代 5003）
     # 強制使用 gunicorn 綁定 port 80 (覆蓋 Dockerfile CMD)
-    command: ["gunicorn", "--bind", "0.0.0.0:80", "--workers", "4", "--timeout", "300", "--access-logfile", "-", "--error-logfile", "-", "app:app"]
+    command: ["gunicorn", "--bind", "0.0.0.0:80", "--workers", "4", "--timeout", "300", "--access-logfile", "-", "--error-logfile", "-", "--preload", "app:app"]
     volumes:
       # 持久化數據
       - ./data:/app/data