feat: Implement a rich text editor using Lexical

- Added RichTextEditor component with basic formatting features.
- Integrated toolbar with undo/redo, text formatting, and color pickers.
- Created EditorTheme for styling the editor components.
- Added styles for editor and toolbar.
- Introduced DropdownColorPicker for color selection.
- Updated package.json to include Lexical dependencies.
- Created EditorDemo page to showcase the rich text editor.
- Added README documentation for the editor's features and usage.

src/editor/index.ts

@@ -0,0 +1 @@
+export { default } from './RichTextEditor';