fix: add Tailwind CSS entry point for Nuxt UI v3

Nuxt UI v3 with Tailwind v4 requires an explicit CSS import.
Without it, the entry CSS is empty (0 bytes).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/assets/css/main.css

@@ -0,0 +1,2 @@
+@import "tailwindcss";
+@import "@nuxt/ui";

nuxt.config.ts

@@ -3,6 +3,7 @@ export default defineNuxtConfig({
   future: { compatibilityVersion: 4 },
   ssr: false,
   modules: ['@nuxt/ui'],
+  css: ['~/assets/css/main.css'],
 
   runtimeConfig: {
     adminPassword: process.env.ADMIN_PASSWORD || 'admin',