Consolidate white_label to remove_branding and add embed widget

- Rename white_label feature to remove_branding across frontend/backend
- Update billing catalog, plan features, and permission checks
- Add dark mode support to Recharts tooltips with useDarkMode hook
- Create embeddable booking widget with EmbedBooking page
- Add EmbedWidgetSettings for generating embed code
- Fix Appearance settings page permission check
- Update test files for new feature naming
- Add notes field to User model

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

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

frontend/src/components/marketing/FeatureComparisonTable.tsx

@@ -53,8 +53,7 @@ const FEATURE_CATEGORIES = [
     features: [
       { code: 'custom_domain', label: 'Custom domain' },
       { code: 'custom_branding', label: 'Custom branding' },
-      { code: 'remove_branding', label: 'Remove "Powered by"' },
-      { code: 'white_label', label: 'White label' },
+      { code: 'remove_branding', label: 'Remove branding' },
     ],
   },
   {