feat(loyalty): add full i18n support for all loyalty module pages

Replace hardcoded English strings across all 22 templates, 10 JS files,
and 4 locale files (en/fr/de/lb) with ~300 translation keys per language.
Uses server-side _() for Jinja2 templates and I18n.t() for JS toast
messages and dynamic Alpine.js expressions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/loyalty/static/store/js/loyalty-enroll.js

@@ -80,7 +80,7 @@ function storeLoyaltyEnroll() {
                     loyaltyEnrollLog.info('Customer enrolled successfully:', response.card_number);
                 }
             } catch (error) {
-                Utils.showToast(`Enrollment failed: ${error.message}`, 'error');
+                Utils.showToast(I18n.t('loyalty.store.enroll.enrollment_failed', {message: error.message}), 'error');
                 loyaltyEnrollLog.error('Enrollment failed:', error);
             } finally {
                 this.enrolling = false;