feat: Light and dark theme support for the text editor #394

Description

@openworkflowspec/text-editor currently has no theme control. TextEditor creates Monaco with no theme option, so it always renders in Monaco's default.

Add a prop that resolves to a Monaco theme

Motivation

We need to support both light and dark themes.

Proposed Implementation

Use the diagram editor as a reference point as we also implement a prop there and keep in mind, eventually this text editor will be a split screen between the diagram and the text editor.

Definition of Done

• Implementation: Fully implemented according to the Open 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.