fix(i18n): sweep hardcoded 'en-US' from non-loyalty JS to I18n.locale

Follow-up to dd1f9af8 which fixed loyalty. The same hardcoded 'en-US'
in toLocaleDateString / toLocaleString / Intl.NumberFormat appeared in
13 files across catalog, marketplace, orders, tenancy, inventory,
monitoring, cms, the storefront layout, and the shared Utils helper
itself. After this sweep, no non-loyalty JS hardcodes 'en-US' anymore;
all use I18n.locale and respect the user's dashboard language.

The highest-leverage one is static/shared/js/utils.js (Utils.formatDate
/ Utils.formatDateTime / Utils.formatCurrency / Utils.formatNumber) —
those four helpers are called from across the frontends so this one
edit fixes most secondary callsites for free.

Codemod scope was conservative: only replaced 'en-US' when it
appeared as the first argument to toLocale* or new Intl.* calls, to
avoid touching unrelated occurrences (none found, but the guard
matters if more get added).

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

static/shared/js/utils.js

@@ -15,7 +15,7 @@ const Utils = {
 
         try {
             const date = new Date(dateString);
-            return date.toLocaleDateString('en-US', {
+            return date.toLocaleDateString(I18n.locale, {
                 year: 'numeric',
                 month: 'short',
                 day: 'numeric'
@@ -36,7 +36,7 @@ const Utils = {
 
         try {
             const date = new Date(dateString);
-            return date.toLocaleString('en-US', {
+            return date.toLocaleString(I18n.locale, {
                 year: 'numeric',
                 month: 'short',
                 day: 'numeric',
@@ -59,7 +59,7 @@ const Utils = {
         if (amount === null || amount === undefined) return '-';
 
         try {
-            return new Intl.NumberFormat('en-US', {
+            return new Intl.NumberFormat(I18n.locale, {
                 style: 'currency',
                 currency: currency
             }).format(amount);
@@ -76,7 +76,7 @@ const Utils = {
      */
     formatNumber(num) {
         if (num === null || num === undefined) return '0';
-        return num.toLocaleString('en-US');
+        return num.toLocaleString(I18n.locale);
     },
 
     /**