fix(i18n): convert remaining $t() to server-side _() and fix store dashboard language

- Convert storefront enrollment $t() calls to server-side _() to silence
  dev-toolbar warnings (welcome bonus + join button)
- Fix store base template I18n.init() to use current_language (from middleware)
  instead of dashboard_language (hardcoded store config) so language changes
  take effect immediately
- Switch admin loyalty routes to use get_admin_context() for proper i18n support
- Switch store loyalty routes to use core get_store_context() from page_context
- Pass program object to storefront enrollment context for server-side rendering
- Add LANG-011 architecture rule: enforce $t()/_() over I18n.t() in templates
- Fix duplicate file_pattern key in LANG-004 rule (YAML validation error)

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

app/templates/store/base.html

@@ -84,7 +84,7 @@
         // Wrapped in DOMContentLoaded so deferred i18n.js has loaded
         document.addEventListener('DOMContentLoaded', async function() {
             const modules = {% block i18n_modules %}[]{% endblock %};
-            await I18n.init('{{ dashboard_language | default("en") }}', modules);
+            await I18n.init('{{ current_language | default("en") }}', modules);
         });
     </script>