feat: add initial Slidev presentation and demo components

- Created Slidev presentation structure with index.md and contents.md.
- Implemented footer and menu components for navigation.
- Added Markdown preview component with syntax highlighting.
- Developed HTML template for consistent page structure.
- Introduced button component with variant support.
- Added Vue counter component for interactive demos.
- Configured content collections for documentation.
- Created multiple markdown documents for demo purposes.
- Established global and theme styles for consistent UI.
- Set up TypeScript configuration for better development experience.

solution/slides/pages/contents.md

@@ -0,0 +1,10 @@
+---
+title: '例子'
+---
+
+# 常用语法结构
+
+---
+---
+
+# 第二个