fix(i18n): complete translations for production launch and fix CMS store context

- Replace CMS custom get_store_context() with core utility (same fix as loyalty)
- Add 85 missing translation keys across fr/de/lb for core, tenancy, messaging,
  customers, and loyalty modules
- Convert 21 client-side $t() calls to server-side _() in 9 loyalty templates
- Fix 3 broken translation keys in store/cards.html

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

app/modules/customers/locales/de.json

@@ -32,6 +32,11 @@
             "description": "Nachrichten an Kunden senden"
         }
     },
+    "messages": {
+        "failed_to_toggle_customer_status": "Kundenstatus konnte nicht geändert werden",
+        "failed_to_load_customer_details": "Kundendetails konnten nicht geladen werden",
+        "failed_to_load_customer_orders": "Kundenbestellungen konnten nicht geladen werden"
+    },
     "menu": {
         "store_operations": "Shop-Betrieb",
         "customers_section": "Kunden",