Refuse a script/loadtest clients count that starts with 0

vegeta reads a leading 0 in its worker count as octal, so 00 gave no
workers and 010 gave eight. The clients check before the build now
refuses any value starting with 0, zero included. The duration needs no
change: vegeta reads it as decimal, so 05s is five seconds.

TODO.md: the load test entry is once, at the top of Completed Steps,
and the entries for #206 and
#204 are no longer repeated.

Model: opus-5-5

script/loadtest

@@ -51,8 +51,10 @@ main() {
         "" | *[!0-9]*) usage ;;
     esac
     [ "$number" -gt 0 ] || usage
+    # The number of clients is a whole number that does not start with 0,
+    # which also refuses zero: vegeta reads a leading 0 as octal.
     case "$clients" in
-        *[!0-9]* | 0) usage ;;
+        *[!0-9]* | 0*) usage ;;
     esac
 
     cd "$ROOT"