feat: 实现大书远距目录跳转与后台补全优化方案

Phase 1: 稳定性优先
- 新增 RDEPUBJumpSession 保护机制，防止远距跳转后翻页串章
- 升级页图接管条件，增加 JumpSession 保护区检查
- 窗口扩展改为基于当前权威窗口方向

Phase 2: 补全优先级重排
- 新增 RDEPUBBackgroundPriorityPolicy 策略配置
- 实现 hot/warm/cold zone 优先级排序
- 添加失败重试机制（指数退避，最多3次）

Phase 3: 分段覆盖与最终收敛
- 新增 RDEPUBBackgroundCoverageStore 分段存储
- 新增 RDEPUBPageMapReconciliationCoordinator 页图接管仲裁
- 实现 LRU 淘汰和内存警告处理

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

Sources/RDReaderView/EPUBUI/TextPage/RDEPUBTextContentView.swift

@@ -17,7 +17,8 @@ protocol RDEPUBTextContentViewDelegate: AnyObject {
     func textContentView(
         _ contentView: RDEPUBTextContentView,
         didActivateAttachmentText text: String,
-        sourceRect: CGRect
+        sourceRect: CGRect,
+        sourcePoint: CGPoint
     )
     func textContentView(
         _ contentView: RDEPUBTextContentView,
@@ -552,7 +553,12 @@ final class RDEPUBTextContentView: UIView, UIGestureRecognizerDelegate {
         }
         if let attachmentText = attachmentText(at: point),
            let sourceRect = attachmentSourceRect(at: point, fallbackPoint: point) {
-            delegate?.textContentView(self, didActivateAttachmentText: attachmentText, sourceRect: sourceRect)
+            delegate?.textContentView(
+                self,
+                didActivateAttachmentText: attachmentText,
+                sourceRect: sourceRect,
+                sourcePoint: convert(point, from: overlayView)
+            )
             return
         }
         guard let highlight = highlight(at: point),