Add Gmail --query to mail/sync (default in:inbox) (#4)

* Add --query to Gmail mail/sync instead of always listing in:inbox.

Callers keep the search string; default remains in:inbox.

* Document Gmail --query on the mail/sync pipeline.

* test(mail): assert Gmail --query reaches ListIDs, not only the CLI flag.

ParseCLI coverage left a hole: an empty query still has to become in:inbox
and a custom q has to be the string the client lists with.

AGENTS.md

@@ -52,6 +52,7 @@ var/          kb.lbug, var/mail/*, caches (gitignored)
 
 ```bash
 bin/mail/sync.go --source onlyoffice,gmail --workers 8 --out var/mail   # raw message.json + attachments
+bin/mail/sync.go --source gmail --query 'from:example.com' --out var/mail  # Gmail search (default in:inbox)
 bin/mail/import --from-raw var/mail                                     # message.json → message.md (convert only)
 bin/mail/index_mail                                                     # rebuild brain incl. all mail (fresh DB)
 ```