fix(SAM/react): 할인액/할인율 표시 포맷 수정

- 할인액 0원일 때 -0원 → 0원으로 표시
- 할인율 소수점 있을 시 반올림 처리 (0.00% → 0%)

src/components/orders/documents/ContractDocument.tsx

@@ -207,11 +207,11 @@ export function ContractDocument({
               <td className="p-2 bg-gray-100 border-r border-gray-300 w-32">공급가액</td>
               <td className="p-2 text-right border-r border-gray-300">{formatAmount(subtotal)}</td>
               <td className="p-2 bg-gray-100 border-r border-gray-300 w-32">할인율</td>
-              <td className="p-2 text-right">{discountRate}%</td>
+              <td className="p-2 text-right">{Number.isInteger(discountRate) ? discountRate : Math.round(discountRate)}%</td>
             </tr>
             <tr className="border-b border-gray-300">
               <td className="p-2 bg-gray-100 border-r border-gray-300">할인액</td>
-              <td className="p-2 text-right border-r border-gray-300 text-red-600">-{formatAmount(discountAmount)}</td>
+              <td className="p-2 text-right border-r border-gray-300 text-red-600">{discountAmount > 0 ? `-${formatAmount(discountAmount)}` : formatAmount(discountAmount)}</td>
               <td className="p-2 bg-gray-100 border-r border-gray-300">할인 후 공급가액</td>
               <td className="p-2 text-right">{formatAmount(afterDiscount)}</td>
             </tr>