feat(control): инструмент «Маркер» на области видимости

Добавлена кисть маркера на пульте и презентации с настройками в панели эффектов; штрихи привязаны к жёлтой рамке, ластик и очистка работают с отдельным сессионным слоем.

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

app/shared/sceneMarkerEraser.ts

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+import type { NPoint } from './types/effects';
+import type { SceneMarkerStroke } from './types/sceneMarker';
+
+function distSqPointToSegment(
+  px: number,
+  py: number,
+  x1: number,
+  y1: number,
+  x2: number,
+  y2: number,
+): number {
+  const dx = x2 - x1;
+  const dy = y2 - y1;
+  const len2 = dx * dx + dy * dy;
+  if (len2 < 1e-18) {
+    const ex = px - x1;
+    const ey = py - y1;
+    return ex * ex + ey * ey;
+  }
+  let t = ((px - x1) * dx + (py - y1) * dy) / len2;
+  t = Math.max(0, Math.min(1, t));
+  const qx = x1 + t * dx;
+  const qy = y1 + t * dy;
+  const ex = px - qx;
+  const ey = py - qy;
+  return ex * ex + ey * ey;
+}
+
+function minDistToEraserStroke(
+  p: { x: number; y: number },
+  eraserPoints: readonly { x: number; y: number }[],
+): number {
+  if (eraserPoints.length === 0) return Number.POSITIVE_INFINITY;
+  let bestSq = Number.POSITIVE_INFINITY;
+  for (const ep of eraserPoints) {
+    const dx = p.x - ep.x;
+    const dy = p.y - ep.y;
+    bestSq = Math.min(bestSq, dx * dx + dy * dy);
+  }
+  for (let i = 1; i < eraserPoints.length; i += 1) {
+    const a = eraserPoints[i - 1];
+    const b = eraserPoints[i];
+    if (!a || !b) continue;
+    bestSq = Math.min(bestSq, distSqPointToSegment(p.x, p.y, a.x, a.y, b.x, b.y));
+  }
+  return Math.sqrt(bestSq);
+}
+
+function isPointErased(
+  p: { x: number; y: number },
+  strokeRadiusN: number,
+  eraserPoints: readonly { x: number; y: number }[],
+  eraserRadiusN: number,
+): boolean {
+  const threshold = eraserRadiusN + strokeRadiusN;
+  return minDistToEraserStroke(p, eraserPoints) <= threshold;
+}
+
+function splitKeptPointRuns(
+  points: NPoint[],
+  eraserPoints: readonly { x: number; y: number }[],
+  eraserRadiusN: number,
+  strokeRadiusN: number,
+): NPoint[][] {
+  const runs: NPoint[][] = [];
+  let current: NPoint[] = [];
+  for (const p of points) {
+    if (isPointErased(p, strokeRadiusN, eraserPoints, eraserRadiusN)) {
+      if (current.length > 0) {
+        runs.push(current);
+        current = [];
+      }
+      continue;
+    }
+    current.push(p);
+  }
+  if (current.length > 0) runs.push(current);
+  return runs;
+}
+
+/** Стирает штрихи маркера ластиком (как туман/огонь). */
+export function applySceneMarkerEraserStroke(
+  strokes: readonly SceneMarkerStroke[],
+  eraserPoints: readonly NPoint[],
+  eraserRadiusN: number,
+  makeId: (prefix: string) => string,
+): SceneMarkerStroke[] {
+  if (eraserPoints.length === 0) return [...strokes];
+  const out: SceneMarkerStroke[] = [];
+  for (const stroke of strokes) {
+    const runs = splitKeptPointRuns(stroke.points, eraserPoints, eraserRadiusN, stroke.radiusN);
+    if (runs.length === 0) continue;
+    if (runs.length === 1 && runs[0]?.length === stroke.points.length) {
+      out.push(stroke);
+      continue;
+    }
+    for (const run of runs) {
+      if (run.length === 0) continue;
+      out.push({
+        ...stroke,
+        id: makeId('mk'),
+        points: run,
+      });
+    }
+  }
+  return out;
+}