fix(cms): storefront renders sections for landing pages + fix nav URLs

Two critical fixes for POC site rendering:

1. Storefront content page route now selects template based on
   page.template field: 'full' → landing-full.html (section-based),
   'modern'/'minimal' → their respective templates. Default stays
   content-page.html (plain HTML). Previously always used content-page
   which ignores page.sections JSON.

2. Storefront base_url uses store.subdomain (lowercase, hyphens)
   instead of store.store_code (uppercase, underscores) for URL
   building. Nav links now point to correct paths that the store
   context middleware can resolve.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/core/utils/page_context.py

@@ -384,15 +384,17 @@ def get_storefront_context(
     if access_method == "path" and store:
         platform = getattr(request.state, "platform", None)
         platform_original_path = getattr(request.state, "platform_original_path", None)
+        # Use subdomain (lowercase, hyphens) for URL routing — store_code is for internal use
+        store_slug = store.subdomain or store.store_code
         if platform and platform_original_path and platform_original_path.startswith("/platforms/"):
-            base_url = f"/platforms/{platform.code}/storefront/{store.store_code}/"
+            base_url = f"/platforms/{platform.code}/storefront/{store_slug}/"
         else:
             full_prefix = (
                 store_context.get("full_prefix", "/storefront/")
                 if store_context
                 else "/storefront/"
             )
-            base_url = f"{full_prefix}{store.store_code}/"
+            base_url = f"{full_prefix}{store_slug}/"
 
     # Read subscription info set by StorefrontAccessMiddleware
     subscription = getattr(request.state, "subscription", None)