feat: add CMS service layer and API endpoints

Implement complete CMS business logic and REST API:

Service Layer (content_page_service.py):
- get_page_for_vendor() - Two-tier lookup with fallback
- list_pages_for_vendor() - Merge vendor + platform pages
- create_page(), update_page(), delete_page() - CRUD operations
- Support for published/draft workflow
- Footer/header navigation filtering

API Endpoints:

Admin API (/api/v1/admin/content-pages):
- POST /platform - Create platform defaults
- GET /platform - List platform defaults
- GET / - List all pages with vendor filtering
- PUT /{id} - Update any page
- DELETE /{id} - Delete any page

Vendor API (/api/v1/vendor/{code}/content-pages):
- GET / - List available pages (vendor + platform merged)
- GET /overrides - List only vendor overrides
- POST / - Create vendor override
- PUT /{id} - Update vendor page
- DELETE /{id} - Delete vendor page

Shop API (/api/v1/shop/content-pages):
- GET /navigation - Get footer/header navigation pages
- GET /{slug} - Get specific page (public, with fallback)

All endpoints include proper authentication, authorization,
and validation using Pydantic schemas.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/main.py

@@ -9,7 +9,7 @@ This module provides:
 """
 
 from fastapi import APIRouter
-from app.api.v1 import admin, vendor, public
+from app.api.v1 import admin, vendor, public, shop
 
 api_router = APIRouter()
 
@@ -46,3 +46,14 @@ api_router.include_router(
     tags=["public"]
 )
 
+# ============================================================================
+# SHOP ROUTES (Public shop frontend API)
+# Prefix: /api/v1/shop
+# ============================================================================
+
+api_router.include_router(
+    shop.router,
+    prefix="/v1/shop",
+    tags=["shop"]
+)
+