Support children in schematic sections

[MustafaMulla29]

Summary

• add optional children support to SchematicSectionProps and its Zod schema
• regenerate the public props documentation
• add coverage for parsing nested schematic section children

Why

<schematicsection> is intended to work as a container, similar to <schematicsheet>, but its public prop type and parser did not accept children. This prevented users from expressing section membership by nesting JSX inside the section element.

Impact

Users can type and parse nested children in <schematicsection> elements. The corresponding Core change makes those descendants inherit section membership and participate in section-aware layout.

Validation

• bun test (375 tests passed)
• bun run typecheck
• bun run format:check
• bun run build
• all required documentation generators