fix: loyalty module end-to-end — merchant route, store menus, sidebar, API error handling

- Add merchant loyalty overview route and template (was 404)
- Fix store loyalty route paths to match menu URLs (/{store_code}/loyalty/...)
- Add loyalty rewards card to storefront account dashboard
- Fix merchant overview to resolve merchant via get_merchant_for_current_user_page
- Fix store login to use store's primary platform for JWT token (interim fix)
- Fix apiClient to attach status/errorCode to thrown errors (fixes error.status
  checks in 12+ JS files — loyalty settings, terminal, email templates, etc.)
- Hide "Add Product" sidebar button when catalog module is not enabled
- Add proposal doc for proper platform detection in store login flow

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

app/templates/store/partials/sidebar.html

@@ -106,6 +106,7 @@
         </div>
     </div>
 
+    {% if 'catalog' in enabled_modules %}
     <!-- Quick Actions (static, outside dynamic menu) -->
     <div class="px-6 my-6">
         <button class="flex items-center justify-between w-full px-4 py-2 text-sm font-medium leading-5 text-white transition-colors duration-150 bg-purple-600 border border-transparent rounded-lg active:bg-purple-600 hover:bg-purple-700 focus:outline-none focus:shadow-outline-purple"
@@ -114,6 +115,7 @@
             <span class="ml-2">Add Product</span>
         </button>
     </div>
+    {% endif %}
 </div>
 {% endmacro %}