feat(scenes): add scene darkness reveal and fix project reopen crash

Add darkenScene with Opening brush in presentation, persist reveal strokes per scene during a session, and close projects properly on return to home. Harden dnd asset streaming to avoid Windows main-process crashes when reopening projects.

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

app/main/project/zipStore.ts

@@ -457,6 +457,7 @@ export class ZipProjectStore {
         previewThumbAssetId: null,
         previewVideoAutostart: false,
         previewRotationDeg: 0,
+        darkenScene: false,
       } satisfies Scene);
 
     const next: Scene = {
@@ -472,6 +473,7 @@ export class ZipProjectStore {
         ? { previewVideoAutostart: patch.previewVideoAutostart }
         : null),
       ...(patch.previewRotationDeg !== undefined ? { previewRotationDeg: patch.previewRotationDeg } : null),
+      ...(patch.darkenScene !== undefined ? { darkenScene: patch.darkenScene } : null),
       ...(patch.settings ? { settings: { ...base.settings, ...patch.settings } } : null),
       ...(patch.media ? { media: { ...base.media, ...patch.media } } : null),
       ...(patch.layout ? { layout: { ...base.layout, ...patch.layout } } : null),
@@ -760,6 +762,16 @@ export class ZipProjectStore {
     await this.packZipExclusive(open.cacheDir, open.zipPath);
   }
 
+  async closeOpenProject(): Promise<void> {
+    if (!this.openProject) return;
+    await this.saveNow();
+    await this.waitWhilePacking();
+    await this.projectWriteChain;
+    this.saveQueued = false;
+    this.openProject = null;
+    this.projectSession += 1;
+  }
+
   async renameOpenProject(name: string, fileBaseName: string): Promise<Project> {
     const open = this.openProject;
     if (!open) throw new Error('No open project');
@@ -1123,6 +1135,7 @@ function normalizeScene(s: Scene): Scene {
   );
   const previewThumbAssetId =
     (s as unknown as { previewThumbAssetId?: AssetId | null }).previewThumbAssetId ?? null;
+  const darkenScene = Boolean((s as unknown as { darkenScene?: boolean }).darkenScene);
 
   const rawAudios = Array.isArray(raw.audios) ? raw.audios : [];
   const audios = rawAudios
@@ -1150,6 +1163,7 @@ function normalizeScene(s: Scene): Scene {
     previewThumbAssetId,
     previewVideoAutostart,
     previewRotationDeg,
+    darkenScene,
     layout: layoutIn ?? { x: 0, y: 0 },
     media: {
       videos: raw.videos ?? [],