fix: make URL environment variable work during build

vite.config.ts

@@ -1,15 +1,21 @@
-import { defineConfig } from 'vite'
+import { defineConfig, loadEnv } from 'vite'
 import react from '@vitejs/plugin-react'
 
 // https://vite.dev/config/
-export default defineConfig({
-  plugins: [react()],
-  define: {
-    __VITE_API_BASE_URL__: "import.meta.env.VITE_API_BASE_URL",
-  },
-  css: {
-    modules: {
-      localsConvention: "camelCase",
-    }
-  },
+export default defineConfig(({ mode }) => {
+  const env = loadEnv(mode, process.cwd(), "");
+
+  return {
+    plugins: [react()],
+    define: {
+      __VITE_API_BASE_URL__: env.VITE_API_BASE_URL
+        ? JSON.stringify(env.VITE_API_BASE_URL)
+        : "undefined",
+    },
+    css: {
+      modules: {
+        localsConvention: "camelCase",
+      }
+    },
+  };
 })