feat: Assess and improve accessibility

[lornakelly]

Description

Run an accessibility audit of the editor, document the violations and define list to fix them

Motivation

Ships as an embeddable npm package so it must not introduce accessibility regressions into host applications. We should verify the repo against a standard (WCAG 2.1 AA)

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.