Log failed logins and refused tokens, address first

For Guard's steward preset and fail2ban: msg="login failed" ip=... user=...
and msg="token refused" ip=..., beside the audit records.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/operations.md

@@ -69,6 +69,22 @@ clients renewing them get a NAK and ask again.
 database when it starts, and an older one refuses a database a newer one
 has upgraded: restore a backup to go back.
 
+## Failed logins in the journal
+
+A failed login to the web UI or the API, and a refused API token, are
+written to the journal as well as the audit log, with the address first:
+
+```
+level=WARN msg="login failed" ip=203.0.113.9 user=admin reason="wrong username or password"
+level=WARN msg="token refused" ip=203.0.113.9 reason="wrong token secret"
+```
+
+Guard's `steward` preset, or a fail2ban filter, can ban such addresses at
+the firewall (with Housecarl's ban lists). The address comes before the
+user name, which a caller chooses, so a pattern anchored on
+`msg="login failed" ip=` can't be fooled by a name. With `log.format:
+json` they are JSON objects with the same fields in the same order.
+
 ## Checks
 
 `stewardd check` validates the configuration in the database against