Request body for creating a fact. Mirrors the fact representation: topic_id,
response_type, template_id, and user_id are always required (the user must have an
active membership in the workspace's organisation), and the type-specific value goes in
the nested value object. justification, begins_at, and ends_at are accepted per
the template's configuration.

The value shape depends on response_type:

• detail answers (number, currency, date, date_range, external, rich_text, unrestricted): { "response": "..." }
• links (link_with_status): { "href": "...", "status": "approved" }
• assessments: { "scale_value_id": 1 } (choice) or { "score": 3.2 } (multistep)
• partnerships (stakeholder): { "stakeholder": "<uuid>", "role": "..." } or { "partner_user_id": 1, "role": "..." }