feat: update user retrieval and add new users table; enhance MainForm with user fetching and localization support

frontend/src/utils/i18n/locales/de/de.json

@@ -8,5 +8,7 @@
     "street": "Straße + Haus Nr.",
     "postal-code": "Plz + Stadt",
     "email": "E-Mail",
-    "submit": "Kaufen"
+    "submit": "Kaufen",
+    "failed-to-load-users": "Das Laden der Benutzer ist fehlgeschlagen.",
+    "user": "Benutzer"
 }

frontend/src/utils/i18n/locales/en/en.json

@@ -8,5 +8,7 @@
     "street": "Street + House No.",
     "postal-code": "Postal Code + City",
     "email": "Email",
-    "submit": "Buy"
+    "submit": "Buy",
+    "failed-to-load-users": "Failed to load users.",
+    "user": "User"
 }

frontend/src/utils/sender.ts

@@ -12,7 +12,6 @@ interface FormData {
   street: string;
   postalCode: string;
   paymentMethod: string;
-  code: string;
 }
 
 export const submitFormData = async (data: FormData) => {