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>

app/templates/vendor/landing-minimal.html

@@ -0,0 +1,67 @@
+{# app/templates/vendor/landing-minimal.html #}
+{# Minimal Landing Page Template - Ultra Clean #}
+{% extends "shop/base.html" %}
+
+{% block title %}{{ vendor.name }}{% endblock %}
+{% block meta_description %}{{ page.meta_description or vendor.description or vendor.name }}{% endblock %}
+
+{% block content %}
+<div class="min-h-screen flex items-center justify-center bg-gradient-to-br from-gray-50 to-gray-100 dark:from-gray-900 dark:to-gray-800">
+    <div class="max-w-3xl mx-auto px-4 sm:px-6 lg:px-8 text-center py-20">
+
+        {# Logo #}
+        {% if theme.branding.logo %}
+        <div class="mb-12">
+            <img src="{{ theme.branding.logo }}"
+                 alt="{{ vendor.name }}"
+                 class="h-24 w-auto mx-auto">
+        </div>
+        {% endif %}
+
+        {# Title #}
+        <h1 class="text-5xl md:text-7xl font-bold text-gray-900 dark:text-white mb-8">
+            {{ page.title or vendor.name }}
+        </h1>
+
+        {# Description/Content #}
+        {% if page.content %}
+        <div class="prose prose-lg dark:prose-invert max-w-2xl mx-auto mb-12 text-gray-600 dark:text-gray-300">
+            {{ page.content | safe }}
+        </div>
+        {% elif vendor.description %}
+        <p class="text-xl md:text-2xl text-gray-600 dark:text-gray-300 mb-12 max-w-2xl mx-auto">
+            {{ vendor.description }}
+        </p>
+        {% endif %}
+
+        {# Single CTA #}
+        <div>
+            <a href="{{ base_url }}shop/"
+               class="inline-flex items-center justify-center px-10 py-5 text-xl font-semibold rounded-full text-white bg-primary hover:bg-primary-dark transition-all transform hover:scale-105 shadow-2xl"
+               style="background-color: var(--color-primary)">
+                Enter Shop
+                <svg class="w-6 h-6 ml-3" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M13 7l5 5m0 0l-5 5m5-5H6"></path>
+                </svg>
+            </a>
+        </div>
+
+        {# Optional Links Below #}
+        {% if header_pages or footer_pages %}
+        <div class="mt-16 pt-8 border-t border-gray-200 dark:border-gray-700">
+            <div class="flex flex-wrap justify-center gap-6 text-sm">
+                <a href="{{ base_url }}shop/products" class="text-gray-600 dark:text-gray-400 hover:text-primary transition-colors">
+                    Products
+                </a>
+                {% for page in (header_pages or footer_pages)[:4] %}
+                <a href="{{ base_url }}shop/{{ page.slug }}" class="text-gray-600 dark:text-gray-400 hover:text-primary transition-colors">
+                    {{ page.title }}
+                </a>
+                {% endfor %}
+            </div>
+        </div>
+        {% endif %}
+
+    </div>
+</div>
+{% endblock %}