feat(reader): 实现大书快速进入与增量分页路径

- PaginationCoordinator: 新增 textReflowable 快速进入路径，支持增量章节构建
  与 staged 合并策略，避免整书一次性构建的主线程阻塞
- TextBookBuilder: 重构为支持单章构建与增量合并模式
- ChapterPageCounter: 优化分页计数逻辑，支持章节级分页缓存
- PageFrameFactory: 新增 CoreText 页面帧工厂，提升排版性能
- ReaderContext/ReaderRuntime: 适配增量分页状态管理

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBReaderAssemblyCoordinator.swift

@@ -23,11 +23,13 @@ final class RDEPUBReaderAssemblyCoordinator {
         setupLoadingIndicator(controller.loadingIndicator, in: controller.view)
         setupErrorLabel(controller.errorLabel, in: controller.view)
         controller.delegate?.epubReader(controller, configureTopToolView: controller.topToolView)
+        print("[ReadViewDemo] assembleInterface: dataSource=\(readerView.dataSource != nil ? "set" : "nil"), numberOfPages=\(readerView.numberOfPages())")
     }
 
     /// 外部纯文本图书启动时，加载已保存的书签、高亮和阅读位置，完成分页收尾。
     func finishExternalTextBookLaunchIfNeeded() {
         guard let runtime = context.runtime,
+              let controller = context.controller,
               context.isExternalTextBook else {
             return
         }
@@ -37,7 +39,14 @@ final class RDEPUBReaderAssemblyCoordinator {
             context.activeBookmarks = context.persistence?.loadBookmarks(for: id) ?? []
             context.activeHighlights = context.persistence?.loadHighlights(for: id) ?? []
         }
-        runtime.finishPagination(restoreLocation: restoreLocation)
+
+        if let textBook = controller.textBook {
+            print("[ReadViewDemo] finishExternalTextBook: applying textBook with \(textBook.pages.count) pages")
+            runtime.applyTextBook(textBook, restoreLocation: restoreLocation)
+            print("[ReadViewDemo] finishExternalTextBook: after applyTextBook, numberOfPages=\(context.readerView?.numberOfPages() ?? -1)")
+        } else {
+            runtime.finishPagination(restoreLocation: restoreLocation)
+        }
     }
 
     private func setupReaderView(_ readerView: RDReaderView, in containerView: UIView) {