add Tailwind and design tokens to frontend.

Tailwind v4 via Vite plugin, theme tokens in main.css, and VS Code hints for v4 at-rules.

frontend/vite.config.ts

@@ -1,5 +1,6 @@
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
+import tailwindcss from '@tailwindcss/vite';
 import { defineConfig } from 'vite';
 import vue from '@vitejs/plugin-vue';
 
@@ -11,8 +12,5 @@ export default defineConfig({
             '@': path.resolve(__dirname, 'src')
         }
     },
-    plugins: [vue()],
-    server: {
-        port: 5173
-    }
+    plugins: [vue(), tailwindcss()]
 });