feat: Apply error page styling (UX)

[lornakelly]

Description

Apply the final visual styling to the error state UI once the component library and design approach are agreed.

Motivation

Ensure error states are visually consistent with the rest of the editor and provide a clear, polished user experience

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.