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/Button.tsx

@@ -24,7 +24,7 @@ const Button: React.FC<ButtonProps & React.ButtonHTMLAttributes<HTMLButtonElemen
   type = 'button',
   ...props 
 }) => {
-  const baseClasses = `inline-flex items-center justify-center font-medium transition-colors duration-200 focus:outline-hidden focus:ring-2 ${isDarkMode ? 'focus:ring-blue-400' : 'focus:ring-blue-500'} focus:ring-offset-1 ${disabled ? 'opacity-50 cursor-not-allowed' : 'cursor-pointer'}`;
+  const baseClasses = `inline-flex items-center justify-center font-medium transition-colors duration-200 focus:outline-none focus:ring-2 ${isDarkMode ? 'focus:ring-blue-400' : 'focus:ring-blue-500'} focus:ring-offset-2 ${disabled ? 'opacity-50 cursor-not-allowed' : 'cursor-pointer'}`;
   
   const variantClasses = {
     text: isDarkMode