feat: setup Tailwind CSS and initial routing structure

Configure @tailwindcss/vite in Nuxt config
Add default layout and main CSS file
Create initial index and login pages
Replace default Nuxt welcome screen with page routing

nuxt.config.ts

@@ -1,6 +1,12 @@
+import tailwindcss from '@tailwindcss/vite'
+
 // https://nuxt.com/docs/api/configuration/nuxt-config
 export default defineNuxtConfig({
   compatibilityDate: '2025-07-15',
   devtools: { enabled: true },
-  modules: ['@nuxt/ui']
-})
+  modules: ['@nuxt/ui'],
+  css: ['~/assets/css/main.css'],
+  vite: {
+    plugins: [tailwindcss()]
+  }
+})