feat: save games and edit scene darkness

Persist show state to local saves; author map darkness in scene editor with bake-to-scene and help updates.

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

app/main/effects/sceneMarkerStore.ts

@@ -105,4 +105,30 @@ export class SceneMarkerStore {
       }
     }
   }
+
+  exportByCard(): Record<string, SceneMarkerStroke[]> {
+    if (this.currentKey !== null) {
+      this.cache.set(this.currentKey, this.state.strokes.map(cloneStroke));
+    }
+    const out: Record<string, SceneMarkerStroke[]> = {};
+    for (const [key, strokes] of this.cache) {
+      if (strokes.length === 0) continue;
+      out[key] = strokes.map(cloneStroke);
+    }
+    return out;
+  }
+
+  importByCard(byCard: Record<string, SceneMarkerStroke[]>): void {
+    this.cache.clear();
+    this.currentKey = null;
+    this.state = emptyState();
+    for (const [key, strokes] of Object.entries(byCard)) {
+      if (!Array.isArray(strokes) || strokes.length === 0) continue;
+      this.cache.set(key, strokes.map(cloneStroke));
+    }
+  }
+}
+
+function cloneStroke(stroke: SceneMarkerStroke): SceneMarkerStroke {
+  return { ...stroke, points: stroke.points.map((p) => ({ ...p })) };
 }