feat: 实现设备注册和精准控制功能，支持双屏管理；更新相关逻辑以优化设备状态跟踪

backend/app/routers.py

@@ -73,6 +73,8 @@ class StateBody(BaseModel):
 class DisplayCommandBody(BaseModel):
     action: str
     params: dict = Field(default_factory=dict)
+    screen_id: str = ""    # 目标屏幕唯一 client_id（精确到某台）
+    screen_role: str = ""  # main | secondary（按角色定位）
 
 
 class ChatMessage(BaseModel):
@@ -487,13 +489,28 @@ _VALID_DISPLAY_ACTIONS = {
 }
 
 
+class RegisterBody(BaseModel):
+    device_id: str = ""    # 唯一设备标识（MQTT client_id）
+    role: str = ""         # main | secondary
+    parent_id: str = ""    # 副屏从属的主屏 device_id；主屏为空
+
+
+@router.post("/api/display/register")
+async def display_register(body: RegisterBody):
+    """设备注册：前端上报唯一 device_id + 角色 + 从属主屏，后端维护设备表供精准控制。"""
+    hub.register_device(body.device_id, body.role, body.parent_id)
+    return {"ok": True, "device_id": body.device_id, "role": body.role, "parent_id": body.parent_id}
+
+
 @router.post("/api/display/command")
 async def display_command_publish(body: DisplayCommandBody):
     """管理端/任意客户端通过 REST 发控制指令 → 后端转 MQTT 广播给所有大屏"""
     if body.action not in _VALID_DISPLAY_ACTIONS:
         return JSONResponse({"ok": False, "error": f"不支持的指令: {body.action}"}, status_code=400)
-    cmd = hub.publish_command(body.action, body.params)
+    # 按屏幕终端路由：screen_id 精确到某客户端；screen_role 按主/副定位；皆空 → 全局广播
+    cmd = hub.publish_command(body.action, body.params, body.screen_id or None, body.screen_role or None)
     return {"ok": cmd.get("published", False), "cmd_id": cmd["cmd_id"], "action": body.action,
+            "screen_id": body.screen_id or "", "screen_role": body.screen_role or "both",
             "mqtt_connected": hub.connected}