Incur derives `--schema`, the `--llms` manifests, and help synopses from
Zod's output view, where a defaulted field always has a value, so every
defaulted argument and option was listed as required even though the CLI
accepts its omission. Wrap each field that fills an omitted value as
optional after registration, keeping its default, constraints, metadata,
and parsed value.
Fixes#1169
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>