fix: clear media live session when leaving live tab

Same-route tab switches do not unmount MediaView, so drop active
play state, heartbeat, and viewer lease when leaving 直播中心.

src/views/MediaView/MediaView.vue

@@ -89,6 +89,7 @@ watch(
   (v) => { if (v) view.value = v }
 )
 
+
 function setView(v) {
   if (!v || route.query.view === v) return
   router.push({ name: 'media', query: { view: v } })
@@ -268,6 +269,18 @@ async function download(v) {
   }
 }
 
+// 同路由 tab 切换不会卸载组件；离开直播中心时必须清播放态/心跳/viewer lease
+watch(view, async (next, prev) => {
+  if (prev === 'live' && next !== 'live') {
+    openSeq += 1
+    await closeActiveLive()
+    return
+  }
+  if (next === 'live' && prev && prev !== 'live') {
+    await load()
+  }
+})
+
 onMounted(load)
 onBeforeUnmount(() => {
   openSeq += 1