feat: add show_in_legal category for bottom bar CMS pages

Add third placement category for content pages that appear in the
bottom bar alongside the copyright notice (Privacy Policy, Terms, etc.):

Model changes:
- Add show_in_legal boolean field to ContentPage model
- Add to to_dict() serialization

Service changes:
- Add legal_only filter to list_pages_for_vendor()

Platform changes:
- Fetch legal_pages in get_platform_context()
- Update base.html to render legal_pages dynamically
- Fallback to hardcoded links if no CMS pages configured

Migration:
- Add column with default=False
- Auto-set show_in_legal=True for privacy and terms pages

Categories:
- show_in_header: Top navigation
- show_in_footer: Quick Links column
- show_in_legal: Bottom bar with copyright (NEW)

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

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

app/templates/platform/base.html

@@ -251,12 +251,21 @@
                         {{ _("platform.footer.copyright", year=2025) }}
                     </p>
                     <div class="flex space-x-6 mt-4 md:mt-0">
-                        <a href="/privacy" class="text-gray-600 dark:text-gray-400 hover:text-primary text-sm transition-colors">
-                            {{ _("platform.footer.privacy") }}
-                        </a>
-                        <a href="/terms" class="text-gray-600 dark:text-gray-400 hover:text-primary text-sm transition-colors">
-                            {{ _("platform.footer.terms") }}
-                        </a>
+                        {% if legal_pages %}
+                            {% for page in legal_pages %}
+                            <a href="/{{ page.slug }}" class="text-gray-600 dark:text-gray-400 hover:text-primary text-sm transition-colors">
+                                {{ page.title }}
+                            </a>
+                            {% endfor %}
+                        {% else %}
+                            {# Fallback to hardcoded links if no CMS pages #}
+                            <a href="/privacy" class="text-gray-600 dark:text-gray-400 hover:text-primary text-sm transition-colors">
+                                {{ _("platform.footer.privacy") }}
+                            </a>
+                            <a href="/terms" class="text-gray-600 dark:text-gray-400 hover:text-primary text-sm transition-colors">
+                                {{ _("platform.footer.terms") }}
+                            </a>
+                        {% endif %}
                     </div>
                 </div>
             </div>