refactor: migrate state imports from contexts to stores directory

src/stores/sidebar/index.ts

@@ -0,0 +1,11 @@
+/**
+ * @file Sidebar 公共导出
+ *
+ * 状态机重构后：
+ *   - reducer 逻辑已合并到 sidebar-machine.ts
+ *   - 类型由 sidebar-types.ts 重新导出
+ *   - React 入口为 sidebar-context.tsx（useMachine 包装）
+ */
+export * from "./sidebar-context";
+export * from "./sidebar-types";
+export { sidebarMachine } from "./sidebar-machine";