Keep the AS list when the asupdate generator fails (closes #173)

make asupdate piped the generator into gzip, so the target saw gzip's
exit status. A failed download replaced pkg/asinfo/asdata.json.gz with
an empty file and the target still exited 0.

The target now runs the new script/asupdate. It writes the generator's
output to a temporary file and checks that the generator succeeded and
wrote at least one AS. Only then does it compress the list and move it
into place. Otherwise it leaves the file alone and exits non-zero.

The generator reads as.csv from ipverse/as-metadata, the source's new
name. The list it builds there is unchanged, so no new list is
committed.

Model: opus-5-5

TODO.md

@@ -33,6 +33,11 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: `make asupdate` runs the new `script/asupdate`. It replaces the AS
+  list built into RouteWatch only when the generator succeeds and finds at least
+  one AS. A failed download used to replace the list with an empty file. The
+  generator reads `as.csv` from `ipverse/as-metadata`, the source's new name
+  (closes #173)
 - 2026-10-27: the WHOIS details of an AS at RIPE, APNIC or AFRINIC come only
   from its `aut-num` object and the organisation object it names. RIPE and APNIC
   start their answer with the `as-block` object of the AS's block. Its dates