fix(embed): scroll freeze — pointer pause leaked when release happened outside window

Root cause: pointerup/pointercancel bound only on the viewport element; press on a photo then release outside the 195x280 window (or gesture interruption) never cleared the 'pointer' pause reason -> auto-scroll stopped permanently until page refresh.
- pointerdown now setPointerCapture (release guaranteed to return)
- window-level pointerup/pointercancel + blur fallbacks clear the reason
- rAF frame wrapped in try/catch so a single bad frame can no longer break the animation chain

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

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

@@ -219,6 +219,14 @@ function onPointerDown(event: PointerEvent): void {
   const anchor = (event.target as HTMLElement).closest<HTMLElement>('a.stream-photo');
   lockedTarget = anchor === null ? null : (anchor.dataset.photoId ?? null);
   setReason('pointer', true);
+  // 指针捕获（滚动卡死修复 2026-09-23）：按下后拖出窗外松开时 viewport 收不到
+  // pointerup，'pointer' 暂停原因会永久残留 → 滚动停死。捕获后 up/cancel 必回
+  // 本元素；window 级兜底监听（onMounted）双保险。
+  try {
+    viewportEl.value?.setPointerCapture(event.pointerId);
+  } catch {
+    /* 指针已释放等：忽略 */
+  }
 }
 
 function onPointerMove(event: PointerEvent): void {
@@ -336,8 +344,21 @@ function onFocusOut(): void {
   }, RESUME_DELAY_MS);
 }
 
+// window 级兜底（滚动卡死修复 2026-09-23）：pointerup 落在窗外/别的元素、
+// 或整个 iframe 失焦（弹框抢焦点）时也要清 pointer 原因，避免暂停态永久卡住。
+function onWindowPointerEnd(): void {
+  if (pointerDownY !== null) onPointerUp();
+}
+function onWindowBlur(): void {
+  pointerDownY = null;
+  setReason('pointer', false);
+}
+
 onMounted(() => {
   document.addEventListener('visibilitychange', onVisibilityChange);
+  window.addEventListener('pointerup', onWindowPointerEnd);
+  window.addEventListener('pointercancel', onWindowPointerEnd);
+  window.addEventListener('blur', onWindowBlur);
   onVisibilityChange();
   if (typeof IntersectionObserver !== 'undefined' && viewportEl.value !== null) {
     visibilityObserver = new IntersectionObserver(
@@ -354,6 +375,9 @@ onBeforeUnmount(() => {
   setReason('destroyed', true);
   layerEl.value?.clear();
   document.removeEventListener('visibilitychange', onVisibilityChange);
+  window.removeEventListener('pointerup', onWindowPointerEnd);
+  window.removeEventListener('pointercancel', onWindowPointerEnd);
+  window.removeEventListener('blur', onWindowBlur);
   visibilityObserver?.disconnect();
   if (resumeTimer !== null) clearTimeout(resumeTimer);
   if (manualClearTimer !== null) clearTimeout(manualClearTimer);