fix: add CORS and HMR config to vite for cross-origin Docker setup

The app is served on port 80 while Vite runs on 5173. The React
plugin needs proper CORS and HMR host config to inject its preamble.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vite.config.js

@@ -19,5 +19,10 @@ export default defineConfig({
         port: 5173,
         strictPort: true,
         origin: 'http://localhost:5173',
+        cors: true,
+        hmr: {
+            host: 'localhost',
+            port: 5173,
+        },
     },
 });