feat: add Markdown editor and preview components
- Implemented MarkdownEditor component for editing markdown with support for formatting (bold, italic, underline) and keyboard shortcuts.
- Created MarkdownMaster component to manage the overall markdown editing interface, including action buttons and format toolbar.
- Developed MarkdownPreview component to render the markdown content as HTML.
- Established markdown context store to manage state related to markdown editing, including active formats and configuration.
- Integrated resizable panes for both editor and preview sections for better user experience.
- Added utility components for textarea and resizable functionality.
- Implemented server-side logic for loading and saving problem descriptions in markdown format.
- Enhanced the editor page to handle locked problems and provide user feedback on save actions.