Configure Vercel deployment and preserve deployed theme support

frontend/vite.config.js

@@ -3,6 +3,9 @@ import react from "@vitejs/plugin-react";
 
 export default defineConfig({
   plugins: [react()],
+  define: {
+    "import.meta.env.VITE_MAX_UPLOAD_MB": JSON.stringify(process.env.VERCEL === "1" ? 4 : 20),
+  },
   server: {
     port: 5173,
     proxy: {
@@ -13,4 +16,3 @@ export default defineConfig({
     },
   },
 });
-