feat: Live preview - text edits drive diagram refresh #226

Description

Wire text edits to diagram refresh: edits re-parse the content (debounced) and redraw the diagram, reusing the existing parseWorkflow → buildDiagramElements pipeline. One-way only (text → diagram).

Motivation

Closing the loop so edits are immediately reflected visually, which is the core value of an editor over a static visualiser

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.