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/RDURLReaderController.swift

@@ -25,6 +25,12 @@ import UIKit
 /// navigationController?.pushViewController(controller, animated: true)
 /// ```
 public final class RDURLReaderController: UIViewController {
+    private struct PendingDemoPageRequest {
+        let pageNumber: Int
+        let animated: Bool
+        var attemptCount: Int
+    }
+
     /// 书籍文件 URL
     private let bookURL: URL
     /// EPUB 阅读器配置（字体、行距、主题等）
@@ -41,6 +47,10 @@ public final class RDURLReaderController: UIViewController {
         label.text = "reader=opening"
         return label
     }()
+    private var pendingDemoPageRequest: PendingDemoPageRequest?
+    private var isRetryingPendingDemoPage = false
+    private let maxPendingDemoPageAttempts = 24
+    private let pendingDemoPageRetryDelay: TimeInterval = 0.25
 
     /// 初始化方法
     /// - Parameters:
@@ -88,9 +98,12 @@ public final class RDURLReaderController: UIViewController {
     /// - Returns: 是否成功跳转
     @discardableResult
     public func goToDemoPage(_ pageNumber: Int, animated: Bool = false) -> Bool {
-        let moved = readerController?.go(toPageNumber: pageNumber, animated: animated) ?? false
+        let moved = performDemoPageNavigation(pageNumber, animated: animated)
         if moved {
-            emitDemoState(prefix: "page=\(pageNumber)")
+            pendingDemoPageRequest = nil
+            isRetryingPendingDemoPage = false
+        } else {
+            queuePendingDemoPageNavigation(pageNumber, animated: animated)
         }
         return moved
     }
@@ -187,6 +200,73 @@ public final class RDURLReaderController: UIViewController {
         embeddedController as? RDEPUBReaderController
     }
 
+    @discardableResult
+    private func performDemoPageNavigation(_ pageNumber: Int, animated: Bool) -> Bool {
+        guard let readerController else { return false }
+        guard pageNumber > 0 else { return false }
+
+        let totalPages = readerController.textBook?.pages.count ?? readerController.activePages.count
+        let numPages = readerController.readerView.numberOfPages()
+        print("[ReadViewDemo] performDemoPageNavigation(\(pageNumber)): textBook.pages=\(totalPages), readerView.numberOfPages=\(numPages), currentPage=\(readerController.readerView.currentPage)")
+        guard pageNumber <= totalPages else { return false }
+
+        readerController.readerView.transitionToPage(pageNum: pageNumber - 1, animated: animated)
+        print("[ReadViewDemo] performDemoPageNavigation(\(pageNumber)): after transition, currentPage=\(readerController.readerView.currentPage)")
+        emitDemoState(prefix: "page=\(pageNumber)")
+        return true
+    }
+
+    private func queuePendingDemoPageNavigation(_ pageNumber: Int, animated: Bool) {
+        if let pendingDemoPageRequest,
+           pendingDemoPageRequest.pageNumber == pageNumber,
+           pendingDemoPageRequest.animated == animated {
+            return
+        }
+
+        pendingDemoPageRequest = PendingDemoPageRequest(
+            pageNumber: pageNumber,
+            animated: animated,
+            attemptCount: 0
+        )
+        retryPendingDemoPageIfNeeded()
+    }
+
+    private func retryPendingDemoPageIfNeeded() {
+        guard !isRetryingPendingDemoPage else { return }
+        guard pendingDemoPageRequest != nil else { return }
+
+        isRetryingPendingDemoPage = true
+        DispatchQueue.main.asyncAfter(deadline: .now() + pendingDemoPageRetryDelay) { [weak self] in
+            self?.attemptPendingDemoPageNavigation()
+        }
+    }
+
+    private func attemptPendingDemoPageNavigation() {
+        guard var pendingDemoPageRequest else {
+            isRetryingPendingDemoPage = false
+            return
+        }
+
+        if performDemoPageNavigation(pendingDemoPageRequest.pageNumber, animated: pendingDemoPageRequest.animated) {
+            self.pendingDemoPageRequest = nil
+            isRetryingPendingDemoPage = false
+            return
+        }
+
+        pendingDemoPageRequest.attemptCount += 1
+        if pendingDemoPageRequest.attemptCount >= maxPendingDemoPageAttempts {
+            self.pendingDemoPageRequest = nil
+            isRetryingPendingDemoPage = false
+            print("[ReadViewDemo] automation page=\(pendingDemoPageRequest.pageNumber) failed after \(pendingDemoPageRequest.attemptCount) attempts")
+            return
+        }
+
+        self.pendingDemoPageRequest = pendingDemoPageRequest
+        DispatchQueue.main.asyncAfter(deadline: .now() + pendingDemoPageRetryDelay) { [weak self] in
+            self?.attemptPendingDemoPageNavigation()
+        }
+    }
+
     /// 输出当前阅读器状态日志（Demo 调试用）
     private func logDemoState(prefix: String) {
         guard let readerController else { return }
@@ -259,7 +339,13 @@ public final class RDURLReaderController: UIViewController {
 }
 
 extension RDURLReaderController: RDEPUBReaderDelegate {
+    public func epubReader(_ reader: UIViewController, didOpen publication: RDEPUBPublication) {
+        retryPendingDemoPageIfNeeded()
+        emitDemoState()
+    }
+
     public func epubReader(_ reader: UIViewController, didUpdateLocation location: RDEPUBLocation) {
+        retryPendingDemoPageIfNeeded()
         emitDemoState()
     }