Add Tailwind CSS and Nuxt UI imports

- Create app/assets/css/main.css with required imports
- Configure nuxt.config.ts to load main.css
- Fix missing CSS styling issue
- Following Nuxt UI v4 setup documentation

nuxt4/nuxt.config.ts

@@ -9,5 +9,7 @@ export default defineNuxtConfig({
     '@nuxt/image',
     '@nuxt/eslint',
     '@nuxt/content'
-  ]
+  ],
+
+  css: ['~/assets/css/main.css']
 })