refactor(device): device 表→device_liveness + liveness 接口只返 bool(review 意见)

- 表/类改名 device→device_liveness / Device→DeviceLiveness:该表记的是无障碍存活监控状态
  (心跳/liveness_state/kill_alert_pending/推送目标),非设备信息(品牌/型号),原名误导。同步改
  建表迁移表名/索引/约束(未部署→直接改建表迁移,非加 rename);API 路径 /api/v1/device 不变。
- GET /device/liveness 的 LivenessOut 只返 kill_alert_pending 一个布尔(原返回 liveness_state/
  ever_protected/last_heartbeat_at 等设备详情);前端本就只读 kill_alert_pending,不受影响。

app/models/device.py

@@ -28,10 +28,12 @@ from sqlalchemy.orm import Mapped, mapped_column
 from app.db.base import Base
 
 
-class Device(Base):
-    __tablename__ = "device"
+class DeviceLiveness(Base):
+    # 表名不叫 device:device 易被当成「设备信息(品牌/型号/系统)」表;本表实为**无障碍存活监控状态**
+    # (心跳 last_heartbeat_at + liveness_state + kill_alert_pending + 推送目标 registration_id),故名 device_liveness。
+    __tablename__ = "device_liveness"
     __table_args__ = (
-        UniqueConstraint("user_id", "device_id", name="uq_device_user_device"),
+        UniqueConstraint("user_id", "device_id", name="uq_device_liveness_user_device"),
     )
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
@@ -84,6 +86,6 @@ class Device(Base):
 
     def __repr__(self) -> str:  # pragma: no cover
         return (
-            f"<Device id={self.id} user_id={self.user_id} "
+            f"<DeviceLiveness id={self.id} user_id={self.user_id} "
             f"device_id={self.device_id} state={self.liveness_state}>"
         )