{"service":"sam_zero_app","endpoints":{"detect_frame":"POST /detect/frame  (客户端推送 JPEG/base64 帧，推荐)","detect":"GET /detect  (最近一次检测结果)","video_stream":"GET /video/stream  (MJPEG，需后台检测或已推送帧)","health":"GET /health"},"fields":{"center_pct":"目标中心 [x%, y%]","offset_x_pct":"水平偏差%，0=居中","offset_y_pct":"垂直偏差%，0=居中","center_distance_pct":"距完全居中%，0=完全居中"}}