fix(travel-proxy): 온디맨드 썸네일 폴백 시 has_thumb DB 동기화 + 미사용 import 정리

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

travel-proxy/app/main.py

@@ -9,7 +9,7 @@ from fastapi.responses import FileResponse
 from pydantic import BaseModel
 from PIL import Image
 
-from .db import init_db, get_photos_by_region, get_all_albums, set_album_cover, get_album_cover
+from .db import init_db, get_photos_by_region, get_all_albums, set_album_cover, mark_thumb_done
 from .indexer import sync
 
 logger = logging.getLogger(__name__)
@@ -88,6 +88,7 @@ def _ensure_thumb_fallback(src: Path, album: str) -> Path:
                 fmt = (im.format or "").upper() or "JPEG"
             im.save(tmp, format=fmt, quality=85, optimize=True)
         tmp.replace(out)
+        mark_thumb_done(album, src.name)
         return out
     finally:
         try: