Add unit tests for left-panel SettingsComponent

[Yicong-Huang]

Task Summary

frontend/src/app/workspace/component/left-panel/settings/settings.component.spec.ts exists but its body is currently a placeholder. Renders the workspace's left-panel Settings tab. The spec file currently contains only the license header — no describe / it blocks. Add real test cases against the current component/service shape.

Follow-up to the Vitest migration umbrella #4861; placeholder specs were intentionally left out of #4880's scope so #4880 can track real spec migrations and these can be sized individually.

Task Type

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