feat(effects): add Darkness action effect like freeze

Adds a fullscreen darkness vignette on click and a permanent shadow spot with a black radial gradient (40% edge, 100% center). Includes control panel UI, i18n, eraser support, and tests.

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

app/shared/effectEraserHitTest.test.ts

@@ -34,6 +34,33 @@ void test('pickEraseTargetId: вода по штриху как туман', ()
   assert.equal(id, 'w1');
 });
 
+void test('pickEraseTargetId: тьма как заморозка — точка удара', () => {
+  const darkness: EffectInstance = {
+    ...base,
+    id: 'd1',
+    type: 'darkness',
+    at: { x: 0.4, y: 0.55 },
+    intensity: 1,
+    lifetimeMs: 820,
+  };
+  const id = pickEraseTargetId([darkness], { x: 0.41, y: 0.55 }, 0.05);
+  assert.equal(id, 'd1');
+});
+
+void test('pickEraseTargetId: shadow с учётом inst.radiusN', () => {
+  const shadow: EffectInstance = {
+    ...base,
+    id: 's1',
+    type: 'shadow',
+    at: { x: 0.5, y: 0.5 },
+    radiusN: 0.08,
+    opacity: 1,
+    lifetimeMs: null,
+  };
+  const id = pickEraseTargetId([shadow], { x: 0.59, y: 0.5 }, 0.02);
+  assert.equal(id, 's1');
+});
+
 void test('minDistSqEffectToPoint: молния — расстояние до отрезка', () => {
   const bolt: EffectInstance = {
     ...base,

app/shared/effectEraserHitTest.ts

@@ -43,13 +43,15 @@ export function minDistSqEffectToPoint(inst: EffectInstance, p: { x: number; y:
     case 'lightning':
     case 'sunbeam':
       return distSqPointToSegment(p.x, p.y, inst.start.x, inst.start.y, inst.end.x, inst.end.y);
-    case 'freeze': {
+    case 'freeze':
+    case 'darkness': {
       const dx = inst.at.x - p.x;
       const dy = inst.at.y - p.y;
       return dx * dx + dy * dy;
     }
     case 'scorch':
     case 'ice':
+    case 'shadow':
     case 'poisonCloud': {
       const dx = inst.at.x - p.x;
       const dy = inst.at.y - p.y;
@@ -61,7 +63,7 @@ export function minDistSqEffectToPoint(inst: EffectInstance, p: { x: number; y:
 }
 
 function eraseHitThresholdSq(inst: EffectInstance, toolRadiusN: number): number {
-  if (inst.type === 'scorch' || inst.type === 'ice' || inst.type === 'poisonCloud') {
+  if (inst.type === 'scorch' || inst.type === 'ice' || inst.type === 'shadow' || inst.type === 'poisonCloud') {
     const r = toolRadiusN + inst.radiusN;
     return r * r;
   }

app/shared/types/effects.ts

@@ -3,6 +3,7 @@ export type EffectToolType =
   | 'fire'
   | 'rain'
   | 'water'
+  | 'darkness'
   | 'lightning'
   | 'sunbeam'
   | 'poisonCloud'
@@ -14,12 +15,14 @@ export type EffectInstanceType =
   | 'fire'
   | 'rain'
   | 'water'
+  | 'darkness'
   | 'lightning'
   | 'sunbeam'
   | 'poisonCloud'
   | 'freeze'
   | 'scorch'
-  | 'ice';
+  | 'ice'
+  | 'shadow';
 
 /** Нормализованные координаты (0..1) относительно области предпросмотра/презентации. */
 export type NPoint = { x: number; y: number; tMs: number; pressure?: number };
@@ -65,6 +68,13 @@ export type WaterInstance = EffectInstanceBase & {
   lifetimeMs: number | null;
 };
 
+export type DarknessInstance = EffectInstanceBase & {
+  type: 'darkness';
+  at: { x: number; y: number };
+  intensity: number;
+  lifetimeMs: number;
+};
+
 export type LightningInstance = EffectInstanceBase & {
   type: 'lightning';
   start: { x: number; y: number };
@@ -119,17 +129,28 @@ export type IceInstance = EffectInstanceBase & {
   lifetimeMs: number | null;
 };
 
+export type ShadowInstance = EffectInstanceBase & {
+  /** Внутренний инстанс: тёмное пятно после эффекта «Тьма». */
+  type: 'shadow';
+  at: { x: number; y: number };
+  radiusN: number;
+  opacity: number;
+  lifetimeMs: number | null;
+};
+
 export type EffectInstance =
   | FogInstance
   | FireInstance
   | RainInstance
   | WaterInstance
+  | DarknessInstance
   | LightningInstance
   | SunbeamInstance
   | PoisonCloudInstance
   | FreezeInstance
   | ScorchInstance
-  | IceInstance;
+  | IceInstance
+  | ShadowInstance;
 
 export type EffectToolState = {
   tool: EffectToolType;