将 PDF 成品阅读控制器下沉为 RDPDFReaderView SDK，并修复手机横屏单页连续竖滑

SDK 化收尾：
- 新增 RDPDFReaderView 本地 pod（阅读容器、成品控制器、划线/注释、画笔、
  目录/设置面板、主题与持久化契约），Demo 精简为 PDFKit 页面提供者 + 持久化宿主
- Podfile/工程接入 RDPDFReaderView 与 SnapKit，示例书改用 PDF 阅读器示例文件

手机横屏单页竖滑修复：
- cell 高度改为宽度适配后的纸张高度（sizeForItemAt + 宿主按页提供纵横比），
  纵向超出一屏的内容由外层 collectionView 连续滚动承接，不再被裁掉
- 页面内部不再开启同向嵌套的兜底竖向拖动，修复外层滚动被吞、无法滚到下一页
- 修复 applyContentSize 先评估拖动开关后写 contentSize 的顺序缺陷
- 页码按视口中心命中 cell 计算，补 didEndDragging 兜底；旋转重锚点与
  transitionToPage 改用真实布局位置
- 横竖屏同为竖滑时也重建 cell 并刷新全部可见页的适配配置
- 横屏单页点击不再跳页，只显隐工具栏；翻页交给连续竖滑

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ReadViewDemo/ReadViewDemoUITests/Helpers/AccessibilityIdentifiers.swift

@@ -38,6 +38,30 @@ enum IDs {
     static let readerNoteReturn = "epub.reader.note.return"
     static let readerNoteOpen = "epub.reader.note.open"
 
+    // MARK: - Image PDF text selection and annotations
+
+    /// PDF demo currently retains the legacy EPUB content identifier for compatibility.
+    /// The text layer is the precise, image-coordinate based interaction surface.
+    static let pdfTextLayer = "pdf.reader.text.layer"
+    static let pdfOCRStatus = "pdf.reader.ocr.status"
+    /// PDF 选区菜单与 EPUB 相同，使用系统编辑菜单，按菜单项标题（复制/高亮/注释）定位。
+    static let pdfSelectionMenuCopy = "复制"
+    static let pdfSelectionMenuHighlight = "高亮"
+    static let pdfSelectionMenuAnnotate = "注释"
+    static let pdfCopyStatus = "pdf.reader.copy.status"
+
+    static let pdfAnnotations = "pdf.reader.annotations"
+    static let pdfAnnotationsPanel = "pdf.reader.annotations.panel"
+    static let pdfAnnotationsTable = "pdf.reader.annotations.table"
+    static let pdfAnnotationsFilter = "pdf.reader.annotations.filter"
+    static let pdfAnnotationsEmpty = "pdf.reader.annotations.empty"
+    static func pdfAnnotationRow(_ id: String) -> String { "pdf.reader.annotations.row.\(id)" }
+
+    static let pdfAnnotationEditor = "pdf.reader.annotation.editor"
+    static let pdfAnnotationInput = "pdf.reader.annotation.input"
+    static let pdfAnnotationSave = "pdf.reader.annotation.save"
+    static let pdfAnnotationCancel = "pdf.reader.annotation.cancel"
+
     static let readerSearch = "epub.reader.search"
     static let searchBar = "epub.reader.search.bar"
     static let searchField = "epub.reader.search.field"