feat(insta-lab): 슬레이트 zip 패키지 다운로드 API (10 PNG + caption.txt)

GET /api/insta/slates/{slate_id}/package 엔드포인트 추가.
렌더된 card_assets PNG들 + suggested_caption + hashtags를
단일 zip으로 번들해 StreamingResponse 반환.
hashtags JSON 문자열/리스트 방어 파싱 포함.

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

insta-lab/app/test_package_api.py

@@ -0,0 +1,45 @@
+import io, os, tempfile, zipfile, sys
+from fastapi.testclient import TestClient
+
+
+def _client(monkeypatch):
+    # Insert web-backend root (3 levels up from this file) so _shared is importable
+    sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
+    from app import config, db
+    tmp = tempfile.mkdtemp()
+    monkeypatch.setattr(config, "INSTA_DATA_PATH", tmp, raising=False)
+    monkeypatch.setattr(db, "DB_PATH", os.path.join(tmp, "insta.db"), raising=False)
+    db.init_db()
+    from app.main import app
+    return TestClient(app), db, tmp
+
+
+def test_package_zip_contains_pngs_and_caption(monkeypatch):
+    client, db, tmp = _client(monkeypatch)
+    # 슬레이트 + 2개 asset(실제 PNG 파일) 시드
+    sid = db.add_card_slate({
+        "keyword": "k",
+        "category": "economy",
+        "status": "rendered",
+        "cover_copy": {"headline": "h"},
+        "body_copies": [{"headline": "b", "body": "x"}] * 8,
+        "cta_copy": {},
+        "suggested_caption": "캡션입니다",
+        "hashtags": ["#a", "#b"],
+    })
+    cards_dir = os.path.join(tmp, "insta_cards", str(sid))
+    os.makedirs(cards_dir, exist_ok=True)
+    for pg in (1, 2):
+        fp = os.path.join(cards_dir, f"{pg:02d}.png")
+        with open(fp, "wb") as f:
+            f.write(b"\x89PNG\r\n" + b"0" * 2000)
+        db.add_card_asset(slate_id=sid, page_index=pg, file_path=fp)
+    r = client.get(f"/api/insta/slates/{sid}/package")
+    assert r.status_code == 200
+    assert r.headers["content-type"] == "application/zip"
+    z = zipfile.ZipFile(io.BytesIO(r.content))
+    names = z.namelist()
+    assert any(n.endswith(".png") for n in names)
+    assert "caption.txt" in names
+    cap = z.read("caption.txt").decode("utf-8")
+    assert "캡션입니다" in cap and "#a" in cap