docs: correct the audit header to the database production actually uses (#304)

The header recorded figures from the first run of this script, which went
against the pre-cutover `relaycast` instance rather than `relaycast-cloud`,
the one the worker binds. The deployment figures reported to the design partner
and in the migration record are 4 colliding pair groups, 87 mismatched ids and
2607 two-party conversations; the header said 30 and 3425. The finding
replicated on both instances so the conclusion held, but the numbers in the
script disagreed with every other record of the same run.

Also names which instance the figures come from and how to resolve it (the SST
resource, never the name matching the repo), and adds the missing `--remote` to
the usage example — without it wrangler reads the local emulated database and
the audit reports on nothing.

Comment-only; no behaviour change.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>