feat(scene): shared zoom/pan for control and presentation

Keep effects pinned to map coordinates when the viewport changes; materials/NPC overlays stay screen-fixed.

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

app/renderer/shared/sceneView/useSceneViewState.ts

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