refactor: simplify HTTPS configuration in Vite setup

frontend/vue-app/vite.config.ts

@@ -7,14 +7,16 @@ export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, process.cwd(), '')
   const backendHost = env.VITE_BACKEND_HOST ?? '127.0.0.1'
 
+  const httpsConfig =
+    fs.existsSync('./key.pem') && fs.existsSync('./cert.pem')
+      ? { key: fs.readFileSync('./key.pem'), cert: fs.readFileSync('./cert.pem') }
+      : undefined
+
   return {
     plugins: [vue()],
     server: {
       host: '0.0.0.0',
-      https: {
+      https: httpsConfig,
-        key: fs.readFileSync('./key.pem'),
-        cert: fs.readFileSync('./cert.pem'),
-      },
       proxy: {
         '/api': {
           target: `http://${backendHost}:5000`,