docs(cli): --help's rubrics section drifted to three fields, it has four

Task 5 (celebrant-rubrics-phase1) added a fourth rubrics column,
creed, and updated the man page for it. bin/main.ml's own built-in
--help was not: its "output formats" section and worked example still
showed three fields (date, formulary slug, source), and nothing
caught it because test/cli.t pins command dispatch but never the help
body.

Fixed the format line and its example, and added a short mention of
the creed column to the surrounding prose paragraph (source, format,
what --overlay/--lang/--raw do to it), matching the man page's own
account without copying it verbatim.

test/cli.t now cross-checks --help's own rubrics example against what
`colitur rubrics 2026` actually prints for the identical day, so the
two cannot silently drift apart again in either direction.
Mutation-proved: reverting the field count in --help alone (output
unchanged) reddens exactly this new check; reverted clean.

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