Follow up on active-overlay viewport lifecycle and regression coverage

Context

#454 fixes the freehand selection-outline misalignment during viewport zoom by adding the missing post-layout updateActiveSection refresh.

The fix is intentionally scoped to the current active-host architecture. This issue tracks the two non-blocking follow-ups raised during review.

Follow-ups

• Investigate whether active overlays can be refreshed from one consistent final viewport state, potentially removing the component-level updateActiveSection second pass. This includes reviewing the lifecycle/order between listRender.update(), initializeViewBox(), and updateViewportOffset().

• Add more representative regression coverage using setupTestingBoard / TestingBoardFixture and a real viewport operation such as Transforms.setViewport or BoardTransforms.updateZoom, followed by flushing the change cycle and verifying the freehand active drawing update.

References

• #454
• Review: https://github.com/plait-board/drawnix/pull/454#pullrequestreview-4838174906