Delete the step.

Side effects:

• Removes the step's GUID from the parent task's steps ordering array.
• Cleans up the step's translations.
• If the step is a managed feedback target (auto-created via feedback_config[].linked: true), the linked subtask cascade-deletes too.

If another step's feedback_config[].link was manually wired to this step, that reference is not cleaned up automatically and will remain dangling. The runtime UI refuses to navigate to a missing step, but consumers should consider re-wiring or removing the dangling link.