frontend: replace more superagent with pankow fetcher

frontend/src/filemanager.js

@@ -5,10 +5,10 @@ import './style.css';
 
 import '@fontsource/noto-sans';
 
-import superagent from 'superagent';
-
 import { createRouter, createWebHashHistory } from 'vue-router';
 
+import { fetcher } from 'pankow';
+
 import FileManager from './FileManager.vue';
 import Home from './views/Home.vue';
 import Viewer from './views/Viewer.vue';
@@ -47,10 +47,8 @@ const i18n = createI18n({
 
   async function loadLanguage(lang) {
     try {
-      const result = await superagent.get(`${API_ORIGIN}/translation/${lang}.json`);
-
-      // we do not deliver as application/json :/
-      translations[lang] = JSON.parse(result.text);
+      const result = await fetcher.get(`${API_ORIGIN}/translation/${lang}.json`);
+      translations[lang] = result.body;
     } catch (e) {
       console.error(`Failed to load language file for ${lang}`, e);
     }