fix: pageCurl翻页后偶尔刷新回章节第一页

根因：.extendPartial pageMap更新提交时使用了异步扩展开始时捕获的
currentPageNumber/currentLocation，在pageCurl模式下用户可能已经翻了几页，
导致过时值通过transitionToPage把用户拉回旧位置。

修复三点：
1. PresentationRuntime: .extendPartial fallback不再使用捕获的
   currentPageNumber，改用readerView.currentPage实时值
2. ChapterWarmupOrchestrator: 异步加载完成回调中使用实时位置
   (readerView.currentPage + locationCoordinator.currentVisibleLocation())
   而非异步开始时捕获的旧值
3. PresentationRuntime: rebindVisiblePage在pageCurl模式下，
   如果正在翻页动画中(isPageCurlTransitioning)，延迟到动画结束后
   再用实时currentPage执行transitionToPage，避免在pageNum回调栈
   内同步触发transitionToPage导致重入

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

Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBPresentationRuntime.swift

@@ -248,8 +248,13 @@ final class RDEPUBPresentationRuntime {
                rebindVisibleLocation(currentLocation, readerView: readerView, controller: controller) {
                 return true
             }
+            // Fallback: prefer the live readerView.currentPage over the stale captured
+            // currentPageNumber, which may be outdated by the time this commit runs
+            // (especially in pageCurl mode where the user may have turned several pages
+            // since the extension was initiated).
+            let livePageIndex = max(readerView.currentPage, 0)
             rebindVisiblePage(
-                to: max(currentPageNumber - 1, 0),
+                to: livePageIndex,
                 readerView: readerView
             )
             return true
@@ -264,7 +269,17 @@ final class RDEPUBPresentationRuntime {
 
     private func rebindVisiblePage(to pageIndex: Int, readerView: RDReaderView) {
         if readerView.currentDisplayType == .pageCurl {
-            readerView.transitionToPage(pageNum: pageIndex, animated: false)
+            if readerView.isPageCurlTransitioning {
+                // Defer the transition until the current page-curl animation completes,
+                // and re-read the live page at that time to avoid jumping to a stale position.
+                DispatchQueue.main.async { [weak readerView] in
+                    guard let readerView, !readerView.isPageCurlTransitioning else { return }
+                    let livePageIndex = max(readerView.currentPage, 0)
+                    readerView.transitionToPage(pageNum: livePageIndex, animated: false)
+                }
+            } else {
+                readerView.transitionToPage(pageNum: pageIndex, animated: false)
+            }
         } else {
             readerView.reloadPageCountOnly()
             if pageIndex != readerView.currentPage {