feat: Add node containment support to composite tasks react flow components (do, for, fork, try

[lornakelly]

Description

Add node containment support for composite tasks (do, for, fork, try) within the React Flow diagram. Introduce visually distinct parent nodes that can render their child nodes within their boundaries, reflecting the hierarchical structure of these task types. This will leverage React Flow’s parentId and relative positioning to correctly scope and position child nodes inside their parent. Initial implementation can use default styling, with scope for visual refinement later.

Motivation

Better represent the hierarchical nature of composite tasks in the diagram, making workflows easier to understand by visually grouping related nodes and clarifying execution structure at a glance.

Proposed Implementation

No response

Definition of Done

• Implementation: Fully implemented according to the Serverless Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.