feat(scene): video map editor parity and help updates

Enable scene editor, overlays, effects, and darkness on video scenes; brighten GM trap markers; document snap, NPC types, materials, and control controls in RU/EN help.

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

app/shared/types/containMediaRect.test.ts

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+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { containMediaRect } from './containMediaRect';
+
+void test('containMediaRect: letterboxes 16:9 into square host', () => {
+  const r = containMediaRect({
+    hostW: 400,
+    hostH: 400,
+    mediaW: 1920,
+    mediaH: 1080,
+    scale: 1,
+    ox: 0.5,
+    oy: 0.5,
+  });
+  assert.ok(r);
+  assert.ok(Math.abs(r!.w - 400) < 0.01);
+  assert.ok(Math.abs(r!.h - (400 * 1080) / 1920) < 0.01);
+  assert.ok(Math.abs(r!.x - 0) < 0.01);
+  assert.ok(r!.y > 0);
+});
+
+void test('containMediaRect: zoom grows rect around ox/oy', () => {
+  const base = containMediaRect({
+    hostW: 800,
+    hostH: 450,
+    mediaW: 800,
+    mediaH: 450,
+    scale: 1,
+    ox: 0.5,
+    oy: 0.5,
+  });
+  const zoomed = containMediaRect({
+    hostW: 800,
+    hostH: 450,
+    mediaW: 800,
+    mediaH: 450,
+    scale: 2,
+    ox: 0.5,
+    oy: 0.5,
+  });
+  assert.ok(base && zoomed);
+  assert.ok(zoomed!.w > base!.w);
+  assert.ok(zoomed!.x < base!.x);
+});

app/shared/types/containMediaRect.ts

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+/**
+ * Pure layout math shared by ContainedVideo / RotatedImage contain-mode.
+ * Kept free of DOM so unit tests can lock overlay alignment for video scenes.
+ */
+export function containMediaRect(args: {
+  hostW: number;
+  hostH: number;
+  mediaW: number;
+  mediaH: number;
+  scale: number;
+  ox: number;
+  oy: number;
+}): { x: number; y: number; w: number; h: number } | null {
+  const { hostW, hostH, mediaW, mediaH, scale, ox, oy } = args;
+  if (hostW <= 1 || hostH <= 1 || mediaW <= 0 || mediaH <= 0) return null;
+  const fit = Math.min(hostW / mediaW, hostH / mediaH);
+  const s = fit * Math.max(1, scale);
+  const w = mediaW * s;
+  const h = mediaH * s;
+  return {
+    x: hostW / 2 - ox * w,
+    y: hostH / 2 - oy * h,
+    w,
+    h,
+  };
+}