feat(boxstore): add configurable expiry for one-time downloads

Introduces a new configuration setting `one_time_download_expiry_seconds` to allow administrators to define a default expiration period for one-time downloads.

The retention logic in `boxstore` has been updated to use this global expiry value when a box is marked as a one-time download and no specific retention period is defined in the manifest.

lib/server/server.go

@@ -29,6 +29,7 @@ func Run(addr string) error {
 	}
 
 	boxstore.SetUploadRoot(cfg.UploadsDir)
+	boxstore.SetOneTimeDownloadExpiry(cfg.OneTimeDownloadExpirySeconds)
 
 	store, err := metastore.Open(cfg.DBDir)
 	if err != nil {