chore(dependencies): update Tailwind CSS and related configurations

- Removed @tailwindcss/postcss from devDependencies and updated tailwindcss to version 3.4.15 for improved styling.
- Added autoprefixer as a new dependency to enhance CSS compatibility.
- Updated postcss.config.js to reflect the new Tailwind CSS plugin structure.
- Created a new tailwind.config.js file to define Tailwind's configuration.
- Adjusted CSS imports in index.css to utilize Tailwind's utility classes.
- Refined focus styles across various components for better accessibility and visual consistency.

worklenz-frontend/src/pages/TaskManagementDemo.tsx

@@ -20,7 +20,7 @@ const TaskManagementDemo: React.FC = () => {
 
   return (
     <Layout className="min-h-screen bg-gray-50">
-      <Header className="bg-white shadow-xs">
+      <Header className="bg-white shadow-sm">
         <div className="max-w-7xl mx-auto px-4">
           <Title level={2} className="mb-0 text-gray-800">
             Enhanced Task Management System