Restore --cron warning visibility; show destination on blob upload

--cron used to behave like full quiet mode for everything that
wasn't an error: warnings were swallowed both in the structured
log channel (LevelError gate) and at the snapshot terminus (the
"Finished (with N warnings)" line went through ui.Complete, which
is silenced under SetQuiet). A backup that, say, hit Full Disk
Access permission errors on a handful of files and skipped them
via --skip-errors would exit 0 and emit nothing — the cron job
would never page anyone.

--cron now obeys "silent only on total success":

  * log.Initialize raises the cron/quiet log level from Error to
    Warn so log.Warn output still reaches stdout (and therefore
    cron's mail).
  * The post-backup terminus message switches to ui.Warning when
    WarningCount > 0. Warning is not silenced by SetQuiet, so cron
    delivers the summary line whenever the count is non-zero. The
    no-warnings path keeps ui.Complete, which IS silenced under
    cron — that's the success path.

Separately, blob upload UI now names the actual destination
instead of the generic "backup destination store" string. The
Begin/Info lines emit the storer's reported Location (s3://bucket,
file:///mnt/usb/backup, rclone://remote/path, etc.), so anyone
watching a backup can see exactly where each blob is landing.

internal/snapshot/scanner.go

@@ -1177,16 +1177,17 @@ func (s *Scanner) uploadBlobIfNeeded(ctx context.Context, blobPath string, blobW
 	finishedBlob := blobWithReader.FinishedBlob
 
 	// Check if blob already exists (deduplication after restart)
+	destination := s.storage.Info().Location
 	if _, err := s.storage.Stat(ctx, blobPath); err == nil {
 		log.Info("Blob already exists in storage, skipping upload",
 			"hash", finishedBlob.Hash, "size", humanize.Bytes(uint64(finishedBlob.Compressed)))
-		s.ui.Info("Blob %s (%s) already exists in backup destination store. Skipping upload.",
-			s.ui.Hex(finishedBlob.Hash), s.ui.Size(finishedBlob.Compressed))
+		s.ui.Info("Blob %s (%s) already exists at %s. Skipping upload.",
+			s.ui.Hex(finishedBlob.Hash), s.ui.Size(finishedBlob.Compressed), s.ui.Path(destination))
 		return true, nil
 	}
 
-	s.ui.Begin("Uploading blob %s (%s) to backup destination store.",
-		s.ui.Hex(finishedBlob.Hash), s.ui.Size(finishedBlob.Compressed))
+	s.ui.Begin("Uploading blob %s (%s) to %s.",
+		s.ui.Hex(finishedBlob.Hash), s.ui.Size(finishedBlob.Compressed), s.ui.Path(destination))
 
 	progressCallback := s.makeUploadProgressCallback(ctx, finishedBlob, startTime)