Replace hardcoded French strings with i18n calls

Initialize i18n before auth so t() works when rendering
auth-dependent UI, and build the command palette lazily so
translations are loaded first. Bump service worker cache version.

frontend/js/backup-manager.js

@@ -221,7 +221,7 @@ async function previewBackup(fpath) {
   var content = document.getElementById('bm-preview-content');
   var title = document.getElementById('bm-preview-title');
   panel.style.display = 'block';
-  content.textContent = 'Chargement...';
+  content.textContent = t("common.loading");
 
   try {
     var data = await api('/api/backups/content?path=' + encodeURIComponent(fpath));