Implement interactive text annotation feature:
- Add text selection detection via JavaScript in WebView
- Create AnnotationColorPicker with 4 color options (yellow, green, blue, red)
- Integrate color picker sheet in bookmark detail views
- Calculate text offsets for precise annotation positioning
- Add onTextSelected callback for WebView component
- Prepare UI for future API integration
Users can now select text in articles and choose a highlight color.
API integration for persisting annotations will follow.