fix(server/m7-353): rename unused r in handleAdminBulkRefetchCovers

internal/api/admin_covers.go

@@ -55,7 +55,7 @@ type adminBulkRefetchResp struct {
 // handleAdminBulkRefetchCovers implements POST /api/admin/covers/refetch-missing.
 // Returns immediately; actual drain runs in a background goroutine bounded by
 // the configured backfill cap.
-func (h *handlers) handleAdminBulkRefetchCovers(w http.ResponseWriter, r *http.Request) {
+func (h *handlers) handleAdminBulkRefetchCovers(w http.ResponseWriter, _ *http.Request) {
 	cap := h.coverArtBackfillCap
 	go func() {
 		bgCtx := context.Background()