Epic: Milestone 1 - Side-by-side text + diagram

[lornakelly]

Description

Grow the read-only viewer into a split-view authoring experience: a workflow text editor on one side, the live diagram on the other. Text edits refresh the diagram, and the text editor ships with schema-driven validation/ autocomplete / IntelliSense so the specification is approachable for newcomers and faster to debug for those fixing existing files.

Per the ADR: text (YAML/JSON) stays the source of truth; this milestone is a one-way live preview (text → diagram) - no scroll-follow or text↔diagram selection sync

Motivation

Post-MVP release with real authoring value.

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.