refactor: rename shop to storefront throughout codebase

Rename "shop" to "storefront" as not all platforms sell items -
storefront is a more accurate term for the customer-facing interface.

Changes:
- Rename app/api/v1/shop/ → app/api/v1/storefront/
- Rename app/routes/shop_pages.py → app/routes/storefront_pages.py
- Rename app/modules/cms/routes/api/shop.py → storefront.py
- Rename tests/integration/api/v1/shop/ → storefront/
- Update API prefix from /api/v1/shop to /api/v1/storefront
- Update route tags from shop-* to storefront-*
- Rename get_shop_context() → get_storefront_context()
- Update architecture rules to reference storefront paths
- Update all test API endpoint paths

This is Phase 2 of the storefront module restructure plan.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routes/platform_pages.py

@@ -127,14 +127,14 @@ async def homepage(
 
         if landing_page:
             # Render landing page with selected template
-            from app.routes.shop_pages import get_shop_context
+            from app.routes.storefront_pages import get_storefront_context
 
             template_name = landing_page.template or "default"
             template_path = f"vendor/landing-{template_name}.html"
 
             logger.info(f"[HOMEPAGE] Rendering vendor landing page: {template_path}")
             return templates.TemplateResponse(
-                template_path, get_shop_context(request, db=db, page=landing_page)
+                template_path, get_storefront_context(request, db=db, page=landing_page)
             )
 
         # No landing page - redirect to shop