Edit a survey draft with Kai

Ask Kai to edit the draft. Body { instruction, definition?, selectedId?, lang? }: definition is the editor's working copy (default: the stored draft), selectedId the step "this question" refers to, lang the language the teammate is viewing. Nothing is saved: returns { status: 'edited', summary, definition, changes: [{ kind, step, id, number?, type?, title, details }], warnings, languagesAdded, languagesNotInProject } for review, or { status: 'unrelated' | 'unclear' | 'no_change' | 'failed', message }. Existing questions keep their ids and answer keys. Uses AI credits (402 when out of AI usage); 429 when asked too often.