PR Summary

Medium Risk
Changes the ordering semantics of editor.setSelectedShapes during brush selection, which may affect downstream behaviors that depend on selection order (e.g. grouping/alignment operations). Logic is localized to Brushing but touches core interaction UX.

Overview
Brush selection now preserves a deterministic sweep/entry order for selectedShapeIds instead of using an unordered set.

Brushing tracks when each shape first enters the brush rectangle via a new selectionOrder map and applies that ordering when calling editor.setSelectedShapes, including shift+brush additive selection and cases with no hit-test candidates.

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