feat: Styling tweaks and visual refinements

[lornakelly]

Description

As we continue rendering more real-world workflows in the editor, we will likely need to make iterative styling adjustments to improve overall readability and visual consistency.

The goal is not to introduce major design changes, but to incrementally improve the visual experience as we validate the editor against a wider variety of workflows and edge cases.

Motivation

Initial designs and styling provide a strong foundation, but workflow rendering is highly visual and many refinements only become apparent once larger and more complex workflows are rendered in practice.

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.