Define proxy host variable in vite.config.ts

Add a new line to define the proxy host variable.

web/vite.config.ts

@@ -5,6 +5,7 @@ import react from "@vitejs/plugin-react-swc";
 import monacoEditorPlugin from "vite-plugin-monaco-editor";
 
 const proxyHost = process.env.PROXY_HOST || "localhost:5000";
+
 // https://vitejs.dev/config/
 export default defineConfig({
   define: {