feat: Integrate the language service with Monaco

[fantonangeli]

Description

Integrate @openworkflowspec/language-service with Monaco in @openworkflowspec/text-editor using @volar/monaco.
The integration should expose the language-service capabilities in Monaco

Motivation

Connect the language service to the Monaco-based text editor so schema-driven completions and diagnostics can be used in the TE.

Proposed Implementation

• Add @volar/monaco and @openworkflowspec/language-service integration to the text editor
• Configure the language-service worker lifecycle according to Spike: Decide on approach for language service #209
• Allow worker creation to be configured by the host application
• Enable language-service completions and diagnostics through Monaco

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.