Add weekend open skip, expiry force-close, and Chinese trade labels.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/strategy/__init__.py

@@ -1,4 +1,4 @@
-from .clock import can_open_new, window_key
+from .clock import can_open_new, is_weekend, window_key
 from .exits import check_exits
 from .group import next_group_id
 from .signal import Signal, decide
@@ -10,6 +10,7 @@ __all__ = [
     "check_exits",
     "decide",
     "get_engine",
+    "is_weekend",
     "next_group_id",
     "set_engine",
     "window_key",