feat(compare): 比价记录列表改按创建时间倒序(id 兜底)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/repositories/comparison.py

@@ -135,11 +135,11 @@ def list_records(
     limit: int = 20,
     cursor: int | None = None,
 ) -> tuple[list[ComparisonRecord], int | None]:
-    """比价记录分页(按 id 倒序,游标式)。附「已下单」店级标记(瞬态,不写库)。"""
+    """比价记录分页(按创建时间倒序、id 兜底,游标式)。附「已下单」店级标记(瞬态,不写库)。"""
     stmt = select(ComparisonRecord).where(ComparisonRecord.user_id == user_id)
     if cursor is not None:
         stmt = stmt.where(ComparisonRecord.id < cursor)
-    stmt = stmt.order_by(ComparisonRecord.id.desc()).limit(limit)
+    stmt = stmt.order_by(ComparisonRecord.created_at.desc(), ComparisonRecord.id.desc()).limit(limit)
 
     items = list(db.execute(stmt).scalars().all())
     next_cursor = items[-1].id if len(items) == limit else None