This commit replaces the basic textarea in the 'Add News' modal with a full-featured Markdown editor.
- Adds the `md-editor-v3` dependency.
- Implements the editor within a `ClientOnly` component for client-side rendering.
- Creates a Nuxt plugin to register the `MdEditor` component globally.
- Adjusts the modal to be fullscreen to provide a better user experience for content creation.
