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.

editor/state.ts

@@ -1,6 +1,6 @@
 import type { ImageDocument } from "@core/document";
 import type { Angle, Size, Vec2D } from "@core/geometry";
-import type { ArtboardId, LayerId } from "@core/id";
+import type { ArtboardId, AssetId, LayerId } from "@core/id";
 import type { ToolState } from "./tools";
 import type { TransformSession } from "./transform";
 
@@ -16,12 +16,32 @@ export type SelectionState = {
   layerIds: LayerId[];
 };
 
+export type MaskViewMode = "composite" | "blackWhite" | "alpha" | "overlay";
+
+export type MaskEditState = {
+  targetLayerId: LayerId;
+  maskLayerId: LayerId;
+  viewMode?: MaskViewMode;
+};
+
+export type BrushPreviewState = {
+  position: Vec2D;
+};
+
+export type BrushStrokePreviewState = {
+  layerId: LayerId;
+  assetId: AssetId;
+  source: string;
+};
+
 export type EditorState = {
   viewport: ViewportState;
   selection: SelectionState;
   tools: ToolState;
   transformSession?: TransformSession;
-  maskEditLayerId?: LayerId;
+  maskEdit?: MaskEditState;
+  brushPreview?: BrushPreviewState;
+  brushStrokePreview?: BrushStrokePreviewState;
 };
 
 export type HistorySnapshot = {