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/renderer/shared/effects/useSceneDarknessState.ts

@@ -0,0 +1,31 @@
+import { useEffect, useState } from 'react';
+
+import { ipcChannels } from '../../../shared/ipc/contracts';
+import type { SceneDarknessEvent, SceneDarknessState } from '../../../shared/types';
+import { getDndApi } from '../dndApi';
+
+export function useSceneDarknessState(): readonly [
+  SceneDarknessState | null,
+  { dispatch: (event: SceneDarknessEvent) => Promise<void> },
+] {
+  const api = getDndApi();
+  const [state, setState] = useState<SceneDarknessState | null>(null);
+
+  useEffect(() => {
+    void api.invoke(ipcChannels.sceneDarkness.getState, {}).then((r) => {
+      setState(r.state);
+    });
+    return api.on(ipcChannels.sceneDarkness.stateChanged, ({ state: next }) => {
+      setState(next);
+    });
+  }, [api]);
+
+  return [
+    state,
+    {
+      dispatch: async (event) => {
+        await api.invoke(ipcChannels.sceneDarkness.dispatch, { event });
+      },
+    },
+  ] as const;
+}