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.

package.json

@@ -10,8 +10,15 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@lexical/code": "^0.37.0",
+    "@lexical/list": "^0.37.0",
+    "@lexical/react": "^0.37.0",
+    "@lexical/rich-text": "^0.37.0",
+    "@lexical/selection": "^0.37.0",
+    "@lexical/utils": "^0.37.0",
     "i18next": "^25.5.3",
     "i18next-browser-languagedetector": "^8.2.0",
+    "lexical": "^0.37.0",
     "react": "^19.1.1",
     "react-dom": "^19.1.1",
     "react-i18next": "^16.0.0",