Docs: Update Duo Workflow development docs to reflect duo-cli as executor

Summary

The Duo Workflow development documentation references the Go-based executor (duo-workflow-executor) as one of the four Agent Platform services. However, this is outdated.

Current state:

• The development docs link to duo-workflow-executor (Go-based)
• That repo has not had commits since November 2025
• The actual executor used in CI jobs is @gitlab/duo-cli (Node/TypeScript from gitlab-lsp)

Evidence from CI job logs:

$ npm install -g @gitlab/duo-cli@8.52.0
...
[DuoWorkflowNodeExecutor][1813503] Running workflow
[DuoWorkflowNodeExecutor][1813503] startRequest: mcp_tools=0

Correct documentation exists: The Flow Execution docs correctly state:

"the runner downloads the @gitlab/duo-cli package from the npm registry" "runs the CLI, which uses WebSocket to connect to the GitLab Duo Workflow Service"

Proposal

Update https://docs.gitlab.com/ee/development/duo_workflow/ to:

1. Replace reference to Go-based duo-workflow-executor with @gitlab/duo-cli (from gitlab-lsp)
2. Clarify the four services as:
   • GitLab Rails (UI, API)
   • GitLab Duo Workflow Service (Python, flow orchestration)
   • @gitlab/duo-cli (Node/TypeScript executor from gitlab-lsp)
   • LLM Backend
3. Consider deprecating/archiving the duo-workflow-executor repo if no longer used

Related

• gitlab-lsp CLI package: https://gitlab.com/gitlab-org/editor-extensions/gitlab-lsp/-/tree/main/packages/cli
• Flow execution docs (correct): https://docs.gitlab.com/ee/user/duo_agent_platform/flows/execution/

/cc @bastirehm @mikolaj_wawrzyniak