fix(embed): scroll freeze root cause — drag-set 'manual' pause reason never cleared

setReason('manual', true) fired on >8px drag had no clear path anywhere (wheel/keyboard have 500ms timers; pointer path didn't) — one drag left the reason permanently, stopping auto-scroll until refresh. Now cleared on pointerup, watchdog, and window blur.

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

apps/viewer/src/pages/embed/EmbedStream.vue

@@ -236,6 +236,7 @@ function onPointerDown(event: PointerEvent): void {
     pointerWatchdog = null;
     pointerDownY = null;
     setReason('pointer', false);
+    setReason('manual', false);
     scheduleResume();
   }, POINTER_WATCHDOG_MS);
 }
@@ -259,6 +260,10 @@ function onPointerUp(): void {
     clearTimeout(pointerWatchdog);
     pointerWatchdog = null;
   }
+  // 拖动置位的 'manual' 原因在此清除（滚动卡死根因修复 2026-09-23：拖动 >8px
+  // setReason('manual', true) 此前无任何清除路径——一次拖动后暂停原因永久残留，
+  // 滚动停死到刷新；滚轮/键盘路径各有 500ms 定时清除，拖动漏了）。
+  setReason('manual', false);
   setReason('pointer', false);
   scheduleResume();
 }
@@ -367,6 +372,7 @@ function onWindowPointerEnd(): void {
 function onWindowBlur(): void {
   pointerDownY = null;
   setReason('pointer', false);
+  setReason('manual', false);
 }
 
 onMounted(() => {