fix(manage): HandleReorderUI gibt 400 bei Mismatch zurück

server/backend/internal/httpapi/manage/ui.go

@@ -3,6 +3,7 @@ package manage
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"html/template"
 	"log/slog"
 	"net/http"
@@ -741,7 +742,11 @@ func HandleReorderUI(playlists *store.PlaylistStore, screens *store.ScreenStore,
 			return
 		}
 		if err := playlists.Reorder(r.Context(), playlist.ID, ids); err != nil {
+			if errors.Is(err, store.ErrReorderMismatch) {
+				http.Error(w, "item list mismatch", http.StatusBadRequest)
+			} else {
 				http.Error(w, "db error", http.StatusInternalServerError)
+			}
 			return
 		}
 		notifier.NotifyChanged(screenSlug)