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/sw.js

@@ -1,6 +1,6 @@
 /* ObsiGate Service Worker - PWA v2 with IndexedDB offline support */
 
-const CACHE_VERSION = 'obsigate-v5-pwa';
+const CACHE_VERSION = 'obsigate-v6-i18n';
 const STATIC_CACHE = CACHE_VERSION + '-static';
 const DYNAMIC_CACHE = CACHE_VERSION + '-dynamic';
 const MAX_DYNAMIC_CACHE_SIZE = 100;