refactor: remove underline animation and update styling

- Remove underline-animation UnoCSS shortcut from uno.config.ts
- Update Navbar component to remove underline-animation classes
- Remove inline script for link transition animations
- Add cover images to existing posts
- Update font and date display classes in index pages
- Modify global CSS for iOS rendering optimization

src/styles/global.css

@@ -17,8 +17,8 @@ html::-webkit-scrollbar {
 body {
   --at-apply: 'text-1.6rem';
   /* Fix for iOS browser flash issue */
-  transform: translateZ(0);
-  -webkit-transform: translateZ(0);
+  backface-visibility: hidden;
+  -webkit-backface-visibility: hidden;
 }
 
 h1 {