`missingTargets` checked every positional argument with `existsSync`, so a
`!`-prefixed exclude or a quoted glob could never exist and the command failed
with "no such path(s)" after both tools had run clean. A pattern is now exempt
from the disk check; a genuine typo still fails.

The exclude also now reaches Oxlint. Oxfmt honours a `!pattern` positional
natively; Oxlint, measured on 1.82.0, neither errors nor excludes and lints the
file anyway, so one argument meant two different things across a single
command's two stages. `howells-check`, `howells-fix` and `howells-oxlint`
translate it into `--ignore-pattern`.

Reported from samplize, where a package excluding one generated JSON file could
not go green.