refactor: move mission flow state into game store

src/hooks/useActivityCity.ts

@@ -1,5 +1,5 @@
-import { useMissionFlowStore } from "@/managers/stores/useMissionFlowStore";
+import { useGameStore } from "@/managers/stores/useGameStore";
 
 export function useActivityCity(): boolean {
-  return useMissionFlowStore((state) => state.activityCity);
+  return useGameStore((state) => state.missionFlow.activityCity);
 }

src/hooks/useGameStep.ts

@@ -1,11 +0,0 @@
-import { useSyncExternalStore } from "react";
-import { GameStepManager } from "@/managers/GameStepManager";
-import type { GameStepSnapshot } from "@/types/game";
-
-const manager = GameStepManager.getInstance();
-
-export function useGameStep(): GameStepSnapshot {
-  return useSyncExternalStore(manager.subscribe.bind(manager), () =>
-    manager.getSnapshot(),
-  );
-}