feat: serve images in manual-label UI from static /do-pfm folder

backend/pfm-web-app/src/app/manual-label/page.tsx

@@ -530,7 +530,7 @@ export default function ManualLabelPage() {
           >
             {files[currentIndex] ? (
               <img
-                src={`/api/files?file=${encodeURIComponent(files[currentIndex])}`}
+                src={`/do-pfm/${encodeURIComponent(files[currentIndex])}`}
                 alt={files[currentIndex]}
                 style={{
                   transform: `scale(${scale}) rotate(${rotation}deg)`,