feat: implement dynamic API base URL and add language toggle in MainForm

Co-authored-by: Copilot <copilot@github.com>

frontend/src/utils/sender.ts

@@ -1,3 +1,5 @@
+import { API_BASE } from "../config/api.config";
+
 interface FormData {
   firstName: string;
   lastName: string;
@@ -18,7 +20,7 @@ export const submitFormData = async (data: FormData, username: string) => {
   console.log(data);
   try {
     const response = await fetch(
-      `http://localhost:8004/default/new-entry?username=${username}`,
+      `${API_BASE}/default/new-entry?username=${username}`,
       {
         method: "POST",
         headers: {