fix(i18n): locale-aware date/number formatting in loyalty factories

Dates rendered in English even when the dashboard language was set to
French (or any other locale). The 5 shared loyalty Alpine factories
hardcoded 'en-US' in every toLocaleDateString / toLocaleString /
Intl.NumberFormat call, ignoring the user's selected language.

- Add `I18n.locale` getter to static/shared/js/i18n.js that returns
  the current dashboard language code (en/fr/de/lb). Falls back to
  'en' if I18n isn't initialised yet.
- Replace 'en-US' with I18n.locale in 5 loyalty shared factories:
  loyalty-cards-list, loyalty-card-detail-view, loyalty-transactions-
  list, loyalty-pins-list, loyalty-devices-list.
- Also fix a latent bug in loyalty-transactions-list.formatDateTime
  that called toLocaleDateString with hour/minute opts (silently
  ignored — same bug previously fixed in loyalty-card-detail-view).

Scoped to loyalty per session decision; other modules with the same
hardcoded 'en-US' pattern (catalog, billing, etc.) are tracked as a
follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/loyalty/static/shared/js/loyalty-card-detail-view.js

@@ -177,13 +177,13 @@ function loyaltyCardDetailView(config) {
 
         // Formatting helpers
         formatNumber(num) {
-            return num == null ? '0' : new Intl.NumberFormat('en-US').format(num);
+            return num == null ? '0' : new Intl.NumberFormat(I18n.locale).format(num);
         },
 
         formatDate(dateString) {
             if (!dateString) return 'Never';
             try {
-                return new Date(dateString).toLocaleDateString('en-US', {
+                return new Date(dateString).toLocaleDateString(I18n.locale, {
                     year: 'numeric',
                     month: 'short',
                     day: 'numeric'
@@ -196,7 +196,7 @@ function loyaltyCardDetailView(config) {
         formatDateTime(dateString) {
             if (!dateString) return 'Never';
             try {
-                return new Date(dateString).toLocaleString('en-US', {
+                return new Date(dateString).toLocaleString(I18n.locale, {
                     year: 'numeric',
                     month: 'short',
                     day: 'numeric',