Replace 24 `err: any` error handler types with proper `AxiosError<ApiErrorResponse>` typing. Fix additional `as any` casts and `Record<string, any>` patterns in registration field components, event settings, and portal layout. Create shared `ApiErrorResponse` type for portal app. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>