feat(backend): add is_read fields on OaTask model.

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

backend/app/models/models.py

@@ -897,6 +897,8 @@ class OaTask(Base):
     resolve_source = Column(String(64), nullable=True, comment="解析来源")
     sign_mode = Column(String(8), nullable=True, comment="or/and")
     round_no = Column(Integer, nullable=False, default=1, comment="所属提交轮次")
+    is_read = Column(SmallInteger, nullable=False, default=0, comment="抄送是否已读 0未读 1已读")
+    read_time = Column(DateTime, nullable=True, comment="抄送首次已读时间")
     tenant_no = Column(String(64), nullable=False, default="zkxw", comment="租户编号")
     order_num = Column(Integer, nullable=True, comment="排序号")
     remark = Column(String(512), nullable=True, comment="备注")