chore: remove unused dependencies, enhance scrollbar functionality, and update VSCode settings

- Removed unused `@types/mdast` dependency from package.json and pnpm-lock.yaml.
- Introduced a custom scrollbar component with theme support in Scrollbar.astro.
- Updated Layout.astro to include the new Scrollbar component.
- Enhanced ThemeToggle.astro to dispatch a theme-changed event on toggle.
- Added global scrollbar styles to global.css and created a new scrollbar.css for custom scrollbar styling.
- Updated VSCode settings to improve editor experience and added recommendations for new extensions.

src/styles/global.css

@@ -14,6 +14,13 @@ body {
     --at-apply: 'transition-all duration-500 ease-in-out';
   }
 }
+* {
+  scrollbar-width: none;
+  -ms-overflow-style: none;
+}
+*::-webkit-scrollbar {
+  display: none;
+}
 h1, h2, h3 {
     text-rendering: optimizeLegibility;
   }