Append-only batch create of draft steps in one transaction. Prefer this
over repeated createWorkflowStep calls when building a full graph.

Semantics (not a sync/replace)

• Never deletes existing draft steps
• Server assigns step IDs
• Link with previous_step_alias / parent_step_alias (or UUID variants)
• Aliases resolve in payload order against existing draft steps and
  earlier steps in the same request
• Full placement validation runs once at the end — all succeed or none applied

Pass include=steps to also receive the full editable draft list (same as
single create).

OAuth callers require the workflows:update scope.