feat: 인스타 슬레이트 패키지 다운로드 버튼

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/api.js

@@ -548,6 +548,8 @@ export function getInstaAssetUrl(slateId, page) {
   return `/api/insta/slates/${slateId}/assets/${page}`;
 }
 
+export const instaPackageUrl = (slateId) => `/api/insta/slates/${slateId}/package`;
+
 export function getInstaTask(taskId) {
   return apiGet(`/api/insta/tasks/${encodeURIComponent(taskId)}`);
 }

src/pages/insta/InstaCards.jsx

@@ -11,6 +11,7 @@ import {
   renderInstaSlate,
   deleteInstaSlate,
   getInstaAssetUrl,
+  instaPackageUrl,
   getInstaTask,
   getInstaPrompt,
   putInstaPrompt,
@@ -832,6 +833,9 @@ function SlateDetail({ slate, onDelete, onRender }) {
         </div>
         <div className="ic-detail__actions">
           <button className="ic-btn ic-btn--secondary ic-btn--sm" onClick={onRender}>재렌더</button>
+          <a className="ic-btn ic-btn--secondary ic-btn--sm" href={instaPackageUrl(slate.id)} download>
+            📦 패키지 다운로드 (10장 + 캡션)
+          </a>
           <button className="ic-btn ic-btn--danger ic-btn--sm" onClick={onDelete}>삭제</button>
         </div>
       </div>