feat: complete large-book pagination runtime and UI coverage

Sources/RDReaderView/EPUBUI/RDEPUBReaderController+PublicAPI.swift

@@ -50,8 +50,18 @@ extension RDEPUBReaderController {
     /// 获取当前页的原生文本语义摘要，用于调试和可访问性
     /// - Returns: 包含页码、断行原因、块类型等信息的摘要字符串，无内容时返回 nil
     public func nativeTextSemanticSummary() -> String? {
-        guard let textBook,
-              let page = textBook.page(at: max(readerView.currentPage + 1, 1)) ?? textBook.pages.first else {
+        let resolvedPage: RDEPUBTextPage?
+        if let textBook {
+            resolvedPage = textBook.page(at: max(readerView.currentPage + 1, 1)) ?? textBook.pages.first
+        } else if readerContext.bookPageMap != nil {
+            let absolutePageIndex = max(readerView.currentPage, 0)
+            _ = runtime.prepareOnDemandChapter(forAbsolutePageNumber: absolutePageIndex + 1)
+            resolvedPage = runtime.pageResolver.resolvePage(absolutePageIndex: absolutePageIndex)?.page
+        } else {
+            resolvedPage = nil
+        }
+
+        guard let page = resolvedPage else {
             return nil
         }
 
@@ -242,4 +252,3 @@ extension RDEPUBReaderController {
         runtime.clearSearch()
     }
 }
-