Refactor step types and workflows handling:

- Simplify `StepType` enums by consolidating subtypes into `TaskSubType`, `GatewaySubType`, and `EventType`.
- Update type checks in components and services to use new subtype structures.
- Standardize API paths by removing `/api` prefix.
- Refactor `DiagramEditor` and related components to align with updated type handling.
- Adjust `ConfigurationPanel` for enhanced subtype selection and handling.