功能：ROI绑定算法时校验RTSP地址有效性

截图加载失败时阻止算法绑定并提示"RTSP拉流地址无效"，
通过Canvas截图加载状态逐层传递到算法绑定组件实现校验。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web-antd/src/views/aiot/device/roi/components/RoiCanvas.vue

@@ -21,6 +21,7 @@ const emit = defineEmits<{
   'roi-drawn': [data: { roi_type: string; coordinates: string }];
   'roi-selected': [roiId: string | null];
   'roi-deleted': [roiId: string];
+  'snap-status': [ok: boolean];
 }>();
 
 const wrapper = ref<HTMLDivElement>();
@@ -77,12 +78,14 @@ onUnmounted(() => {
 
 function onImageLoad() {
   loading.value = false;
+  emit('snap-status', true);
   nextTick(() => initCanvas());
 }
 
 function onImageError() {
   loading.value = false;
-  errorMsg.value = '截图加载失败，请确认摄像头正在拉流';
+  errorMsg.value = '截图加载失败，请确认摄像头拉流地址是否有效';
+  emit('snap-status', false);
   // 关键：截图失败也初始化 canvas，使 ROI 区域可见可操作
   nextTick(() => initCanvas());
 }