DS: Callout — address design system audit gaps

[tilucasoli]

Context

Follow-up from packages/remix/DS_AUDIT_REPORT.md (Callout section).

Pending items

• Title support — Add optional String? title / Widget? title above body with stronger typography (e.g. spec.title or bold TextStyle).
• Supplementary actions — Add List<Widget>? actions or Widget? action (bottom or inline).

Files

lib/src/components/callout/callout_widget.dart, styles as needed.