feat: Build minimal React Flow diagram from model

[lornakelly]

Description

Implement the function that maps the workflow model data and graph to the Node[] and Edge[] arrays required by React Flow. For this first iteration nodes should display minimal information - label and task type only. All edges should use the default edge for now. Node positions should be read from the graph model.

Motivation

React Flow requires nodes and edges in a specific format to render a diagram. This is the final step in the pipeline before the diagram can be visualized, mapping the framework-agnostic graph model into React Flow specific structures.

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.