fix: replace deprecated Sass @import with @use

- Change additionalData from @import to @use ... as *
- Eliminates Sass @import deprecation warnings

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

vite.config.ts

@@ -42,7 +42,7 @@ export default ({ command, mode }: ConfigEnv): UserConfig => {
     css: {
       preprocessorOptions: {
         scss: {
-          additionalData: '@import "./src/styles/variables.scss";',
+          additionalData: '@use "./src/styles/variables.scss" as *;',
           javascriptEnabled: true
         }
       }