[Feat] Support bulk pagination defaults in overlays

[samzong]

Summary

• Add module-level overlay pagination defaults with command glob matching.
• Merge bulk defaults before per-command parameter overrides so explicit command defaults still win.
• Document the precedence and example schema.

Closes #34

Verification

• make check
• go test ./internal/codegen/render ./internal/lathecmd
• git diff --check

Compatibility

• Generated CommandSpec defaults can now come from defaults.pagination overlays.
• Catalog/runtime schema is unchanged; runtime still receives only merged CommandSpec values.
• Existing per-command params.<name>.default overlays continue to work and take precedence.

Checklist

• Tests or focused verification cover the changed surface.
• User-facing behavior changes are documented.
• Generated output under internal/generated/, .cache/, and ad-hoc skills/<cli-name>/ directories is not committed.
• Commits are signed off when this is ready to merge.