feat: unify reader chrome state management

- Add RDEPUBReaderUIState struct for centralized UI state model
- Refactor RDEPUBReaderChromeCoordinator with makeUIState() and applyUIState()
- Remove direct UI updates from RDEPUBReaderAnnotationCoordinator
- Consolidate updateBookmarkChrome() into updateReaderChrome()
- Update RDEPUBReaderContext, Runtime, and LocationCoordinator
- Add reader problem fix development checklist documentation

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

Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBReaderAnnotationCoordinator.swift

@@ -38,9 +38,7 @@ final class RDEPUBReaderAnnotationCoordinator {
            controller.readerView.isShowToolView == false {
             controller.readerView.tapCenter()
         }
-        controller.bottomToolView.setAddHighlightEnabled(
-            controller.configuration.allowsHighlights && controller.currentSelection != nil
-        )
+        controller.updateReaderChrome()
         controller.delegate?.epubReader(controller, didChangeSelection: controller.currentSelection)
     }
 
@@ -321,13 +319,6 @@ final class RDEPUBReaderAnnotationCoordinator {
         return controller.restoreReadingLocation(bookmark.location, animated: animated)
     }
 
-    /// 同步顶部书签按钮和底部书签列表按钮的 UI 状态。
-    func updateBookmarkChrome() {
-        guard let controller else { return }
-        controller.topToolView.setBookmarkSelected(currentBookmark() != nil)
-        controller.bottomToolView.setBookmarksEnabled(!controller.activeBookmarks.isEmpty)
-    }
-
     /// 弹出书签管理器，支持查看、跳转和删除书签。
     func presentBookmarksManager() {
         guard let controller else { return }
@@ -468,10 +459,10 @@ final class RDEPUBReaderAnnotationCoordinator {
         guard let currentBookIdentifier = controller.currentBookIdentifier else { return }
         controller.persistence?.saveBookmarks(controller.activeBookmarks, for: currentBookIdentifier)
         controller.delegate?.epubReader(controller, didUpdateBookmarks: controller.activeBookmarks)
-        updateBookmarkChrome()
+        controller.updateReaderChrome()
     }
 
-    private func currentBookmark() -> RDEPUBBookmark? {
+    func currentBookmark() -> RDEPUBBookmark? {
         guard let controller else { return nil }
         guard let location = scopedBookmarkLocation(controller.currentVisibleLocation()) else {
             return nil