feat(build): integrate Tailwind CSS

This commit integrates Tailwind CSS into the project for utility-first styling.

- Adds `tailwindcss` and `@tailwindcss/vite` as dependencies.
- Configures the Vite build process to use the Tailwind plugin.
- Sets up the main CSS entry point to import Tailwind styles.
- Adds a new route and a `TailwindcssDemo` component to verify the setup.

vite.config.ts

@@ -4,17 +4,14 @@ import { defineConfig } from 'vite'
 import vue from '@vitejs/plugin-vue'
 import vueJsx from '@vitejs/plugin-vue-jsx'
 import vueDevTools from 'vite-plugin-vue-devtools'
+import tailwindcss from '@tailwindcss/vite'
 
 // https://vite.dev/config/
 export default defineConfig({
-  plugins: [
-    vue(),
-    vueJsx(),
-    vueDevTools(),
-  ],
+  plugins: [vue(), vueJsx(), vueDevTools(), tailwindcss()],
   resolve: {
     alias: {
-      '@': fileURLToPath(new URL('./src', import.meta.url))
+      '@': fileURLToPath(new URL('./src', import.meta.url)),
     },
   },
 })