fix: lower confidence threshold for small order images

internal/captcha/handler.go

@@ -887,7 +887,12 @@ func (h *Handler) detectYOLO(modelName, imageBase64 string) (*DetectionResult, e
 
 	// YOLO11 输出: [1, 5, 8400] 或 [1, 84, 8400]
 	// 需要转置 + NMS 后处理，坐标从 640x640 缩放到原图尺寸
-	detections := postprocessYOLO(output, origW, origH, 0.25, 0.45)
+	// 对于小图片（order 提示图）使用更低的置信度阈值
+	confThresh := 0.25
+	if origW < 200 || origH < 100 {
+		confThresh = 0.1 // 小图使用更低阈值
+	}
+	detections := postprocessYOLO(output, origW, origH, confThresh, 0.45)
 
 	result := &DetectionResult{
 		Detections: make([]Detection, len(detections)),
@@ -900,7 +905,7 @@ func (h *Handler) detectYOLO(modelName, imageBase64 string) (*DetectionResult, e
 		}
 	}
 
-	fmt.Printf("DEBUG YOLO '%s': detected %d objects, origSize=%dx%d\n", modelName, len(detections), origW, origH)
+	fmt.Printf("DEBUG YOLO '%s': detected %d objects, origSize=%dx%d, confThresh=%.2f\n", modelName, len(detections), origW, origH, confThresh)
 
 	return result, nil
 }