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>

.architecture-rules/language.yaml

@@ -111,11 +111,9 @@ language_rules:
         function languageSelector(currentLang, enabledLanguages) { ... }
         window.languageSelector = languageSelector;
     pattern:
-      file_pattern: "static/shop/js/shop-layout.js"
-      required_patterns:
-        - "function languageSelector"
-        - "window.languageSelector"
-      file_pattern: "static/vendor/js/init-alpine.js"
+      file_patterns:
+        - "static/shop/js/shop-layout.js"
+        - "static/vendor/js/init-alpine.js"
       required_patterns:
         - "function languageSelector"
         - "window.languageSelector"
@@ -247,3 +245,26 @@ language_rules:
     pattern:
       file_pattern: "static/locales/*.json"
       check: "valid_json"
+
+  - id: "LANG-011"
+    name: "Use $t() not I18n.t() in HTML templates"
+    severity: "error"
+    description: |
+      In HTML templates, never use I18n.t() directly. It evaluates once
+      and does NOT re-evaluate when translations finish loading async.
+
+      WRONG (non-reactive, shows raw key then updates):
+        <span x-text="I18n.t('module.key')"></span>
+
+      RIGHT (reactive, updates when translations load):
+        <span x-text="$t('module.key')"></span>
+
+      BEST (server-side, zero flash):
+        <span>{{ _('module.key') }}</span>
+
+      Note: I18n.t() is fine in .js files where it's called inside
+      async callbacks after I18n.init() has completed.
+    pattern:
+      file_pattern: "**/*.html"
+      anti_patterns:
+        - "I18n.t("