This introduces a user-configurable palette for text highlighting. The four default highlight colors can now be customized by the user from an expanded set of predefined colors.
Changes include:
- Added a `PaletteManagerDialog` to allow users to select and save their preferred highlight colors.
- Implemented `saveHighlightPalette` and `loadHighlightPalette` to persist the user's choices.
- The highlighting UI in both vertical and paginated readers now displays the active custom palette.
- Added new `HighlightColor` options.
- Updated JavaScript to support the expanded color set and improve highlight interaction logic.