Get full validation detail for a case

Returns the full creditor-facing validation status for a case, including the resolution area and description for each outstanding item.

When to call: Check validation.needsInfo on GET /cases/{id}. If true, call this endpoint to retrieve the item-level breakdown of what the creditor must supply.

Safety: Only creditor-facing resolution areas are returned. Internal areas (InternalReview, AdminReview) and sensitive fields (Rationale, Confidence) are never exposed.