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/hooks/useEntitlements.ts

@@ -101,7 +101,7 @@ export const FEATURE_CODES = {
   // Boolean features (permissions)
   CAN_ACCEPT_PAYMENTS: 'can_accept_payments',
   CAN_USE_CUSTOM_DOMAIN: 'can_use_custom_domain',
-  CAN_WHITE_LABEL: 'can_white_label',
+  CAN_REMOVE_BRANDING: 'can_white_label',  // Backend field still named can_white_label
   CAN_API_ACCESS: 'can_api_access',
   CAN_USE_SMS_REMINDERS: 'can_use_sms_reminders',
   CAN_USE_MASKED_PHONE_NUMBERS: 'can_use_masked_phone_numbers',