feat: storefront subscription access guard + module-driven nav + URL rename

Add StorefrontAccessMiddleware that blocks storefront access for stores
without an active subscription, returning a multilingual unavailable page
(en/fr/de/lb) for page requests and JSON 403 for API requests. Multi-platform
aware: resolves subscription for detected platform with fallback to primary.

Also includes yesterday's session work:
- Module-driven storefront navigation via FrontendType.STOREFRONT menu declarations
- shop/ → storefront/ URL rename across 30+ templates
- Subscription context (tier_code) passed to storefront templates

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

app/modules/cms/templates/cms/store/content-pages.html

@@ -172,7 +172,7 @@
                                     </template>
                                     <!-- Preview button -->
                                     <a
-                                        :href="`/stores/${storeCode}/shop/${page.slug}`"
+                                        :href="`/stores/${storeCode}/storefront/${page.slug}`"
                                         target="_blank"
                                         class="flex items-center justify-center p-2 text-gray-500 rounded-lg hover:bg-gray-100 dark:text-gray-400 dark:hover:bg-gray-700 transition-colors"
                                         title="Preview"
@@ -278,7 +278,7 @@
                                         <span x-html="$icon('edit', 'w-5 h-5')"></span>
                                     </a>
                                     <a
-                                        :href="`/stores/${storeCode}/shop/${page.slug}`"
+                                        :href="`/stores/${storeCode}/storefront/${page.slug}`"
                                         target="_blank"
                                         class="flex items-center justify-center p-2 text-gray-500 rounded-lg hover:bg-gray-100 dark:text-gray-400 dark:hover:bg-gray-700 transition-colors"
                                         title="Preview"