修复ROI截图功能：改用ZLM同步getSnap直接返回图片

- 重写snap端点：直接调用ZLM的getSnap同步API，传入RTSP源地址，
  流式返回图片字节流，不再依赖异步文件存储
- 前端改为传srcUrl参数给snap接口，不需要先拉流即可截图
- 修复之前async=1导致ZLM返回JSON而非图片的问题

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

web/src/api/cameraConfig.js

@@ -25,6 +25,6 @@ export function stopCamera(id) {
   })
 }
 
-export function getSnapUrl(cameraId) {
-  return `/api/ai/roi/snap?cameraId=${encodeURIComponent(cameraId)}`
+export function getSnapUrl(srcUrl) {
+  return `/api/ai/roi/snap?url=${encodeURIComponent(srcUrl)}`
 }

web/src/views/cameraConfig/roiConfig.vue

@@ -113,10 +113,8 @@ export default {
   mounted() {
     this.cameraId = decodeURIComponent(this.$route.params.cameraId)
     this.srcUrl = this.$route.query.srcUrl || ''
-    const app = this.$route.query.app || ''
-    const stream = this.$route.query.stream || ''
-    if (app && stream) {
-      this.snapUrl = `/api/ai/roi/snap?app=${encodeURIComponent(app)}&stream=${encodeURIComponent(stream)}`
+    if (this.srcUrl) {
+      this.snapUrl = `/api/ai/roi/snap?url=${encodeURIComponent(this.srcUrl)}`
     }
     this.loadRois()
   },
@@ -147,10 +145,8 @@ export default {
       this.drawMode = mode
     },
     refreshSnap() {
-      const app = this.$route.query.app || ''
-      const stream = this.$route.query.stream || ''
-      if (app && stream) {
-        this.snapUrl = `/api/ai/roi/snap?app=${encodeURIComponent(app)}&stream=${encodeURIComponent(stream)}&t=${Date.now()}`
+      if (this.srcUrl) {
+        this.snapUrl = `/api/ai/roi/snap?url=${encodeURIComponent(this.srcUrl)}&t=${Date.now()}`
       }
     },
     onRoiDrawn(data) {