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/backups.js

@@ -180,7 +180,7 @@ function renderMainView() {
   var html =
     '<div class="backup-header">' +
     '<div class="backup-header-left">' +
-    '<h3>Backups</h3>' +
+    '<h3>'+t('backups.title')+'</h3>' +
     '<span class="backup-file-path">' + escapeHtml(state.path) + '</span>' +
     '</div>' +
     '<div class="backup-header-right">' +