feat: Implement volar-service-yaml for YAML language support #322

Description

Implement the YAML language service component for the @openworkflowspec/language-service package. This service wraps yaml-language-server and provides YAML-specific authoring assistance for Open Workflow documents.

Motivation

Providing comprehensive YAML language support with schema-driven completions, validation, and proper indentation handling is essential for delivering a best-in-class authoring experience.

Proposed Implementation

No response

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.