add unit test coverage for ResultExportationComponent

[mengw15]

Task Summary

frontend/src/app/workspace/component/result-exportation/result-exportation.component.ts (codecov ~6%, no spec) — behavior-focused Vitest spec (TestBed + detectChanges()), mocking WorkflowResultExportService. See frontend/TESTING.md.

Behavior to cover

• should create; detectChanges() renders
• onClickExportResult("dataset", dataset) -> calls the export service targeting the dataset destination
• onClickExportResult("local") -> calls the export service targeting local download
• onClickCreateNewDataset() -> triggers the create-new-dataset flow
• ngOnInit initializes the component state

Task Type

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