Returns the read-only field definitions for an expense record that an approver is reviewing. Use this endpoint instead of the regular fields-initialize endpoint when rendering the approver's review screen — it loads the existing expense record by {expenseId}, derives the response shape from the record's own expense type (ReceiptVerification, CarSpecification, SubsistenceAllowance, FoodBenefitsSpecification, or FuelBenefitsSpecification), and marks every field as read-only so the approver can inspect but not edit. Requires the caller to be assigned as an approver in the organization and to be authorised on the specific expense report this record belongs to; otherwise the endpoint returns 404. The 404 is intentionally identical to "expense not found" so approval-access can't be probed.