feat: add platform detail/edit admin UI and service enhancements

- Add platform detail and edit admin pages with templates and JS
- Add ContentPageService methods: list_all_platform_pages, list_all_vendor_defaults
- Deprecate /admin/platform-homepage route (redirects to /admin/platforms)
- Add migration to fix content_page nullable columns
- Refine platform and vendor context middleware
- Add platform context middleware unit tests
- Update platforms.js with improved functionality
- Add section-based homepage plan documentation

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

scripts/validate_architecture.py

@@ -525,7 +525,7 @@ class ArchitectureValidator:
         # These are page-level components that should inherit from data()
         # Allow optional parameters in the function signature
         component_pattern = re.compile(
-            r"function\s+(admin\w+|vendor\w+|shop\w+)\s*\([^)]*\)\s*\{", re.IGNORECASE
+            r"function\s+(admin\w+|vendor\w+|shop\w+|platform\w+)\s*\([^)]*\)\s*\{", re.IGNORECASE
         )
 
         for match in component_pattern.finditer(content):