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/tailwind.config.js

@@ -0,0 +1,29 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: [
+    "./src/**/*.{js,jsx,ts,tsx}",
+    "./public/index.html"
+  ],
+  theme: {
+    extend: {
+      fontFamily: {
+        sans: [
+          '-apple-system',
+          'BlinkMacSystemFont',
+          '"Inter"',
+          'Roboto',
+          '"Helvetica Neue"',
+          'Arial',
+          '"Noto Sans"',
+          'sans-serif',
+          '"Apple Color Emoji"',
+          '"Segoe UI Emoji"',
+          '"Segoe UI Symbol"',
+          '"Noto Color Emoji"'
+        ],
+      },
+    },
+  },
+  plugins: [],
+  darkMode: 'class',
+}