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/components/AssigneeSelector.tsx

@@ -252,7 +252,7 @@ const AssigneeSelector: React.FC<AssigneeSelectorProps> = ({
                   ? 'bg-gray-700 border-gray-600 text-gray-100 placeholder-gray-400 focus:border-blue-500'
                   : 'bg-white border-gray-300 text-gray-900 placeholder-gray-500 focus:border-blue-500'
                 }
-                focus:outline-hidden focus:ring-1 focus:ring-blue-500
+                focus:outline-none focus:ring-1 focus:ring-blue-500
               `}
             />
           </div>