feat: enhance layer masking functionality and brush controls

- Refactor LayersSheet component to support mask editing state and improve layer visibility handling.
- Introduce functions to collect mask layer IDs and count display layers excluding masks.
- Update BrushControls to include mask view mode options and a Done button for exiting mask editing.
- Modify brush session handling to support brush previews when editing masks.
- Implement a new BrushPreviewRenderer for rendering brush strokes with visual feedback.
- Add document geometry utilities for transforming points and resolving layer bounds.
- Ensure proper cleanup of brush preview on pointer leave and other interactions.

commands/dispatcher.ts

@@ -48,5 +48,12 @@ function recordHistory(currentState: AppState, nextState: AppState): AppState {
 }
 
 function snapshot(state: AppState): HistorySnapshot {
-  return { document: state.document, editor: state.editor };
+  return {
+    document: state.document,
+    editor: {
+      ...state.editor,
+      brushPreview: undefined,
+      brushStrokePreview: undefined,
+    },
+  };
 }