add unit test coverage for PanelService

[aglinxinyuan]

Task Summary

Add panel.service.spec.ts covering PanelService, a tiny event bus that exposes two Subject<void> streams (closePanelStream, resetPanelStream) with closePanels() / resetPanels() triggers.

Background

frontend/src/app/workspace/service/panel/panel.service.ts is a dependency-free service (instantiable directly via new PanelService()), so no TestBed wiring is required.

get resetPanelStream() { return this.resetPanelSubject.asObservable(); }
resetPanels() { this.resetPanelSubject.next(); }
get closePanelStream() { return this.closePanelSubject.asObservable(); }
closePanels() { this.closePanelSubject.next(); }

Behavior to pin

Scenario	Contract
subscribe resetPanelStream, call resetPanels()	subscriber fires exactly once
subscribe closePanelStream, call closePanels()	subscriber fires exactly once
stream independence	calling resetPanels() does not emit on closePanelStream, and vice-versa

Subscribe to the stream, invoke the trigger, and assert the emission count (e.g. increment a counter in the subscription). Follow size-formatter.util.spec.ts for the plain describe/it/expect style (ng test).

Scope

• New spec: frontend/src/app/workspace/service/panel/panel.service.spec.ts.
• No production-code changes.

Task Type

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

[anthonychengit]

/take

[anthonychengit]

This task appears to have been completed by #6461 (which closed #6449) and is already on main as commit c0774be98.

The merged panel.service.spec.ts covers:

• reset and close stream emissions;
• stream independence in both directions;
• delivery to multiple subscribers; and
• late-subscriber Subject semantics.

I also verified the current file locally: Prettier and ESLint pass, and all 6 focused tests pass with:

node .yarn/releases/yarn-4.14.1.cjs test --include=src/app/workspace/service/panel/panel.service.spec.ts

There is no remaining code change unique to this issue, so a new PR would duplicate the merged coverage. @aglinxinyuan, could you please close #6262 as completed/duplicate?

[anthonychengit]

/untake