feat: Apply edge styling (UX)

[lornakelly]

Description

Apply the agreed node design to workflow edges. This includes updating their appearance to match the intended UX and ensuring visual consistency with the broader diagram styling.

Motivation

Improve readability and help users more easily follow relationships and flow through the diagr

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.