feat: Implement volar-service-json for JSON language support

[lornakelly]

Description

Implement the JSON language service component for the @openworkflowspec/language-servicei nee package. This service wraps vscode-json-languageservice and provides JSON-specific authoring assistance for Open Workflow documents.

Motivation

Providing robust JSON language support enables developers to author Open Workflow documents with confidence through schema-driven completions and real-time validation

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.