When remote info could not read a snapshot's manifest, the orphan
figures were unknown but the snapshot's row still gave 0 blobs and 0 B,
in the table and in --json. The row's blob count and blob size are now
unknown, and null in --json.
A directory with no manifest, as an interrupted backup leaves, still
shows 0: the orphan figures count its blobs as orphaned, so it
references none.
The constant holding the "unknown" text is renamed from countUnknown to
unknownText, since it now also stands for a size.
Model: opus-5-5
sneak