Replace the existing contenteditable-based markdown editor with a full-featured WYSIWYG editor using @milkdown/crepe. The new implementation provides:
- True WYSIWYG editing experience with instant Markdown syntax rendering
- Slash command menu support for quick formatting
- Code block highlighting and image paste support
- Built-in export to markdown file functionality
Changes include new MilkdownEditor component, updated App.vue integration, theme styling imports, and optimized Vite configuration for the new dependencies.
ydy0615