fix: 修复6个边缘侧问题 + 单元测试

1. 删除 ConfigAgent (与 MQTT 配置更新重叠且未启用)
2. OTA 完整安装流程: 解压tar.gz -> 校验ELF -> 替换二进制 -> systemctl重启
3. StreamManager stopAll 添加 Wait() 防止僵尸进程
4. InferClient socket 读写添加 timeout 防止永久阻塞
5. Heartbeat 集成 NPU 监控 (npu-smi + fallback 脚本)
6. 配置更新时动态重启 ffmpeg 以应用新 fps

internal/infer/client.go

@@ -208,10 +208,17 @@ func (c *Client) send(conn net.Conn, f stream.Frame) error {
 	if err != nil {
 		return err
 	}
+	conn.SetWriteDeadline(time.Now().Add(10 * time.Second))
+	defer conn.SetWriteDeadline(time.Time{})
 	return writeMsg(conn, data)
 }
 
 func (c *Client) recv(conn net.Conn) (*resultMsg, error) {
+	// Set read deadline to prevent blocking forever if inference server hangs
+	// 30s timeout covers even slow NPU inference on large images
+	conn.SetReadDeadline(time.Now().Add(30 * time.Second))
+	defer conn.SetReadDeadline(time.Time{}) // reset after read
+
 	data, err := readMsg(conn)
 	if err != nil {
 		return nil, err