feat(effects): add Closing brush as inverse of Opening brush

Allow covering revealed darkness again during darkened scene sessions.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/shared/types/effects.ts

@@ -11,6 +11,7 @@ export type EffectToolType =
   | 'explosion'
   | 'freeze'
   | 'exploreBrush'
+  | 'closeBrush'
   | 'eraser';
 
 export type EffectInstanceType =

app/shared/types/sceneDarkness.ts

@@ -1,11 +1,22 @@
 import type { NPoint } from './effects';
 
+/** reveal — снимает тьму (Кисть Открытия); cover — возвращает тьму (Кисть Закрытия). */
+export type SceneDarknessStrokeMode = 'reveal' | 'cover';
+
 export type SceneDarknessRevealStroke = {
   id: string;
   seed: number;
   createdAtMs: number;
   points: NPoint[];
   radiusN: number;
+  /** По умолчанию reveal (старые штрихи без поля). */
+  mode?: SceneDarknessStrokeMode;
+};
+
+export type SceneDarknessDraft = {
+  points: NPoint[];
+  radiusN: number;
+  mode?: SceneDarknessStrokeMode;
 };
 
 export type SceneDarknessState = {
@@ -14,9 +25,13 @@ export type SceneDarknessState = {
   enabled: boolean;
   cacheKey: string | null;
   strokes: SceneDarknessRevealStroke[];
-  draft: { points: NPoint[]; radiusN: number } | null;
+  draft: SceneDarknessDraft | null;
 };
 
 export type SceneDarknessEvent =
-  | { kind: 'draft.set'; draft: { points: NPoint[]; radiusN: number } | null }
+  | { kind: 'draft.set'; draft: SceneDarknessDraft | null }
   | { kind: 'stroke.add'; stroke: SceneDarknessRevealStroke };
+
+export function normalizeSceneDarknessStrokeMode(raw: unknown): SceneDarknessStrokeMode {
+  return raw === 'cover' ? 'cover' : 'reveal';
+}