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>

scripts/validate/validate_architecture.py

@@ -3758,6 +3758,19 @@ class ArchitectureValidator:
                             context=line.strip()[:80],
                             suggestion="Use single quotes: x-data='func({{ data|tojson }})'",
                         )
+
+                    # LANG-011: I18n.t() in templates (should use $t() or server-side _())
+                    if "I18n.t(" in line:
+                        self._add_violation(
+                            rule_id="LANG-011",
+                            rule_name="Use $t() not I18n.t() in HTML templates",
+                            severity=Severity.ERROR,
+                            file_path=file_path,
+                            line_number=i,
+                            message="I18n.t() is non-reactive in templates. Use $t() (reactive) or _() (server-side)",
+                            context=line.strip()[:80],
+                            suggestion="Replace I18n.t('key') with $t('key') or {{ _('key') }}",
+                        )
             except Exception:
                 pass  # Skip files that can't be read