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/services/content_page_service.py

@@ -97,6 +97,7 @@ class ContentPageService:
         include_unpublished: bool = False,
         footer_only: bool = False,
         header_only: bool = False,
+        legal_only: bool = False,
     ) -> list[ContentPage]:
         """
         List all available pages for a vendor (includes vendor overrides + platform defaults).
@@ -109,6 +110,7 @@ class ContentPageService:
             include_unpublished: Include draft pages
             footer_only: Only pages marked for footer display
             header_only: Only pages marked for header display
+            legal_only: Only pages marked for legal/bottom bar display
 
         Returns:
             List of ContentPage objects
@@ -124,6 +126,9 @@ class ContentPageService:
         if header_only:
             filters.append(ContentPage.show_in_header == True)
 
+        if legal_only:
+            filters.append(ContentPage.show_in_legal == True)
+
         # Get vendor-specific pages
         vendor_pages = []
         if vendor_id: