add unit test coverage for NzModalCommentBoxComponent

[mengw15]

Task Summary

frontend/src/app/workspace/component/workflow-editor/comment-box-modal/nz-modal-comment-box.component.ts (codecov ~5%, no spec) — Vitest spec (TestBed + detectChanges()), mocking WorkflowActionService, UserService, NzModalRef, NotificationService. See frontend/TESTING.md.

Behavior to cover

• should create; detectChanges() renders
• onClickAddComment() -> adds a comment through workflowActionService for the current user; clears the input after
• empty/whitespace comment -> no add (if guarded)

Task Type

• Refactor / Cleanup
• DevOps / Deployment / CI
• Testing / QA
• Documentation
• Performance
• Other