Add unit tests for the heat-map overlay wiring in WorkflowEditorComponent

### Task Summary

Add unit-test coverage for the heat-map overlay wiring in `WorkflowEditorComponent`, which shipped without specs in the overlay PR (#6213).

### Context

The overlay's pure logic (`heatmap-scoring.ts`, `heatmap-color.ts`) is well covered, but the editor-side wiring is not: ~33% patch coverage on `workflow-editor.component.ts`. Notably, the disable/enable repaint fix lives in this untested layer and has no regression test.

### Required Test

Cover `handleHeatmapOverlay`, `repaintHeatmapColors`, `restoreAllOperatorFills`, and `handleHeatmapHover` (TestBed + mocked graph/status streams + a stubbed paper), including: - a regression test that a disable/enable while the overlay is active repaints operators with heat colors (not the disable grey/white).

### Related

- Umbrella #5772
- Follow-up from PR #6213 (test-coverage advisory)

### Task Type

- [ ] Refactor / Cleanup
- [ ] DevOps / Deployment / CI
- [x] Testing / QA
- [ ] Documentation
- [ ] Performance
- [ ] Other