Add dashboard and navigation translations with date-fns locale support

- Add translations for all dashboard widgets (de, es, fr)
- Add navigation menu translations for all languages
- Create useDateFnsLocale hook for localized date formatting
- Add translate="no" to prevent browser auto-translation
- Update dashboard components to use translation keys

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/hooks/useDateFnsLocale.ts

@@ -0,0 +1,30 @@
+import { useMemo } from 'react';
+import { useTranslation } from 'react-i18next';
+import { Locale } from 'date-fns';
+import { enUS, de, es, fr } from 'date-fns/locale';
+
+const localeMap: Record<string, Locale> = {
+  en: enUS,
+  de: de,
+  es: es,
+  fr: fr,
+};
+
+/**
+ * Hook to get the date-fns locale based on the current i18n language.
+ * Use this with date-fns functions that support locale, like formatDistanceToNow.
+ *
+ * @example
+ * const locale = useDateFnsLocale();
+ * formatDistanceToNow(date, { addSuffix: true, locale });
+ */
+export const useDateFnsLocale = (): Locale => {
+  const { i18n } = useTranslation();
+
+  return useMemo(() => {
+    const lang = i18n.language?.split('-')[0] || 'en';
+    return localeMap[lang] || enUS;
+  }, [i18n.language]);
+};
+
+export default useDateFnsLocale;