feat: implement vendor landing pages with multi-template support and fix shop routing

Major improvements to shop URL routing and vendor landing page system:

## Landing Page System
- Add template field to ContentPage model for flexible landing page designs
- Create 4 landing page templates: default, minimal, modern, and full
- Implement smart root handler to serve landing pages or redirect to shop
- Add create_landing_page.py script for easy landing page management
- Support both domain/subdomain and path-based vendor access
- Add comprehensive landing page documentation

## Route Fixes
- Fix duplicate /shop prefix in shop_pages.py routes
- Correct product detail page routing (was /shop/shop/products/{id})
- Update all shop routes to work with router prefix mounting
- Remove unused public vendor endpoints (/api/v1/public/vendors)

## Template Link Corrections
- Fix all shop template links to include /shop/ prefix
- Update breadcrumb 'Home' links to point to vendor root (landing page)
- Update header navigation 'Home' link to point to vendor root
- Correct CMS page links in footer navigation
- Fix account, cart, and error page navigation links

## Navigation Architecture
- Establish two-tier navigation: landing page (/) and shop (/shop/)
- Document complete navigation flow and URL hierarchy
- Support for vendors with or without landing pages (auto-redirect fallback)
- Consistent breadcrumb and header navigation behavior

## Documentation
- Add vendor-landing-pages.md feature documentation
- Add navigation-flow.md with complete URL hierarchy
- Update shop architecture docs with error handling section
- Add orphaned docs to mkdocs.yml navigation
- Document multi-access routing patterns

## Database
- Migration f68d8da5315a: add template field to content_pages table
- Support template values: default, minimal, modern, full

This establishes a complete landing page system allowing vendors to have
custom marketing homepages separate from their e-commerce shop, with
flexible template options and proper navigation hierarchy.

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

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

docs/frontend/shop/architecture.md

@@ -108,7 +108,21 @@ Layer 1: ROUTES (FastAPI)
 Purpose: Vendor Detection + Template Rendering
 Location: app/routes/shop_pages.py
 
-Example:
+⚠️ ROUTE REGISTRATION (main.py):
+The shop router is mounted at TWO prefixes to support both access methods:
+
+  # main.py
+  app.include_router(shop_pages.router, prefix="/shop", ...)           # Domain/subdomain
+  app.include_router(shop_pages.router, prefix="/vendors/{vendor_code}/shop", ...)  # Path-based
+
+This means routes defined WITHOUT /shop prefix in shop_pages.py:
+  @router.get("/products")  →  /shop/products  OR  /vendors/{code}/shop/products
+
+❌ COMMON MISTAKE: Don't add /shop prefix in route definitions!
+  @router.get("/shop/products")  ❌ WRONG - creates /shop/shop/products
+  @router.get("/products")       ✅ CORRECT - creates /shop/products
+
+Example Route Handler:
   @router.get("/", response_class=HTMLResponse, include_in_schema=False)
   @router.get("/products", response_class=HTMLResponse, include_in_schema=False)
   async def shop_products_page(request: Request):
@@ -164,31 +178,31 @@ Responsibilities:
 The shop frontend supports THREE access methods:
 
 1. **Custom Domain** (Production)
-   URL: https://customdomain.com/products
+   URL: https://customdomain.com/shop/products
    - Vendor has their own domain
    - base_url = "/"
-   - Links: /products, /about, /contact
+   - Links: /shop/products, /shop/about, /shop/contact
 
 2. **Subdomain** (Production)
-   URL: https://wizamart.letzshop.com/products
+   URL: https://wizamart.letzshop.com/shop/products
    - Vendor uses platform subdomain
    - base_url = "/"
-   - Links: /products, /about, /contact
+   - Links: /shop/products, /shop/about, /shop/contact
 
 3. **Path-Based** (Development/Testing)
-   URL: http://localhost:8000/vendor/wizamart/products
+   URL: http://localhost:8000/vendors/wizamart/shop/products
    - Vendor accessed via path prefix
-   - base_url = "/vendor/wizamart/"
-   - Links: /vendor/wizamart/products, /vendor/wizamart/about
+   - base_url = "/vendors/wizamart/"
+   - Links: /vendors/wizamart/shop/products, /vendors/wizamart/shop/about
 
-⚠️ CRITICAL: All template links MUST use {{ base_url }} prefix
+⚠️ CRITICAL: All template links MUST use {{ base_url }}shop/ prefix
 
 Example:
   ❌ BAD:  <a href="/products">Products</a>
-  ✅ GOOD: <a href="{{ base_url }}products">Products</a>
+  ❌ BAD:  <a href="{{ base_url }}products">Products</a>
+  ✅ GOOD: <a href="{{ base_url }}shop/products">Products</a>
 
-  ❌ BAD:  <a href="/contact">Contact</a>
-  ✅ GOOD: <a href="{{ base_url }}contact">Contact</a>
+Note: The router is mounted at /shop prefix in main.py, so all links need shop/ after base_url
 
 How It Works:
   1. VendorContextMiddleware detects access method