chore(dependencies): update Tailwind CSS and related packages for improved styling

- Added @tailwindcss/postcss as a new dependency.
- Updated tailwindcss to version 4.1.11 for enhanced features and performance.
- Upgraded prettier-plugin-tailwindcss to version 0.6.13 for better formatting support.
- Adjusted postcss.config.js to use the new Tailwind CSS plugin structure.
- Removed the obsolete tailwind.config.js file as it is no longer needed.

worklenz-frontend/src/components/Avatar.tsx

@@ -69,7 +69,7 @@ const Avatar: React.FC<AvatarProps> = ({
         src={src}
         alt={name}
         onClick={handleClick}
-        className={`rounded-full object-cover shadow-sm cursor-pointer ${className}`}
+        className={`rounded-full object-cover shadow-xs cursor-pointer ${className}`}
         style={avatarStyle}
       />
     );
@@ -78,7 +78,7 @@ const Avatar: React.FC<AvatarProps> = ({
   return (
     <div 
       onClick={handleClick}
-      className={`rounded-full flex items-center justify-center text-white font-medium shadow-sm cursor-pointer ${className}`}
+      className={`rounded-full flex items-center justify-center text-white font-medium shadow-xs cursor-pointer ${className}`}
       style={avatarStyle}
     >
       {name.charAt(0)?.toUpperCase() || '?'}