feat: localize membership tier display

frontend/src/plugins/api.js

@@ -1,6 +1,7 @@
 import axios from 'axios';
 import { useAuthStore } from '@/features/auth/stores/authStore.js';
 import config from '@/config.js';
+import { i18n } from '@/plugins/i18n.js';
 
 export function useClient() {
   const client = axios.create({
@@ -36,6 +37,8 @@ export function useClient() {
       config.headers.Authorization = `Bearer ${authStore.accessToken}`;
     }
 
+    config.headers['Accept-Language'] = i18n.global.locale.value ?? 'en';
+
     if (config.data instanceof FormData) {
       console.log(`Data is FormData, removing explicit Content-Type header for: ${config.method?.toUpperCase()} ${config.url}`);
       delete config.headers['Content-Type'];