Add platform email templates, staff invitations, and quota tracking

- Add PlatformEmailTemplate model and API for superuser-managed email templates
- Add PlatformStaffInvitation model with email sending via Celery tasks
- Add platform staff invite page and acceptance flow with auto-login
- Add quota tracking models (DailyAppointmentUsage, DailyAPIUsage, StorageUsage)
- Add quota status API endpoints and frontend banners
- Add storage usage service for tenant media tracking
- Fix platform user deletion with raw SQL to handle multi-tenant FK constraints
- Update EditPlatformUserModal with archive/delete buttons
- Update PlatformSidebar with email templates link for superusers
- Configure console email backend and Celery eager mode for local development

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

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

frontend/src/pages/settings/SystemEmailTemplates.tsx

@@ -253,7 +253,7 @@ const SystemEmailTemplates: React.FC = () => {
             ...item,
             props: {
               ...item.props,
-              id: `${item.type}-${index}-${crypto.randomUUID().substring(0, 8)}`,
+              id: `${item.type}-${index}-${Math.random().toString(36).substring(2, 10)}`,
             },
           };
         }