fix: optimize diagnosis output format and fix inconsistency between fault_status and fault_type

1. 输出格式优化:
   - faults中移除冗余的bbox和confidence字段
   - summary中fault_count改名为detection_count

2. fault_status与fault_type逻辑统一:
   - normal状态时fault_type为'none'，不再使用'suspect'
   - abnormal状态时才进行故障类型分类(hotspot/local_overheating/overheat)

3. 修复usage_example.py图像通道问题:
   - YOLO检测使用彩色图，温度提取时再转灰度图

PROGRESS.md

@@ -222,15 +222,13 @@
   "image": "FLIR0150.jpg",
   "detections": [...],
   "faults": [{
-    "bbox": [...],
-    "confidence": 0.995,
     "temp_max": 255.0,
     "fault_status": "abnormal",
     "fault_type": "hotspot"
   }],
   "summary": {
     "status": "fault_detected",
-    "fault_count": 1,
+    "detection_count": 1,
     "abnormal_count": 1
   }
 }