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/billing/featureCatalog.ts

@@ -224,9 +224,9 @@ export const BOOLEAN_FEATURES: FeatureCatalogEntry[] = [
     category: 'branding',
   },
   {
-    code: 'white_label',
-    name: 'White Label',
-    description: 'Remove SmoothSchedule branding completely',
+    code: 'remove_branding',
+    name: 'Remove Branding',
+    description: 'Remove SmoothSchedule branding from customer-facing pages',
     type: 'boolean',
     category: 'branding',
   },