refactor(sidebar): move SidebarPage/BottomNavItem enums to sidebar-state

Move the `SidebarPage` and `BottomNavItem` enum definitions from
`sidebar-machine.ts` to `sidebar-state.ts` to avoid a circular
dependency between the two modules. Since both enums are tightly
coupled to the state shape (they define the value sets of
`currentPage` and `selectedBottomNavItem`), they now live alongside
the state itself.

- Move enum declarations and types from `sidebar-machine.ts` to
  `sidebar-state.ts`
- Update `sidebar-events.ts` import path to reference `sidebar-state`
- Keep `sidebar-machine.ts` re-exporting `SidebarState` and
  `initialState` to preserve its public API

src/stores/sidebar/sidebar-events.ts

@@ -1,7 +1,7 @@
 /**
  * Sidebar 状态机：事件联合
  */
-import type { SidebarPage, BottomNavItem } from "./sidebar-machine";
+import type { SidebarPage, BottomNavItem } from "./sidebar-state";
 
 export type SidebarEvent =
   | {

src/stores/sidebar/sidebar-machine.ts

@@ -11,31 +11,9 @@
  */
 import { setup, assign } from "xstate";
 
-import { SidebarState, initialState } from "./sidebar-state";
+import { BottomNavItem, SidebarState, initialState } from "./sidebar-state";
 import type { SidebarEvent } from "./sidebar-events";
 
-/**
- * Sidebar 页面/底部导航枚举（与原 sidebar-types.ts 保持一致）
- */
-export const SidebarPage = {
-  DefaultView: "defaultView",
-  Profile: "profile",
-  Topics: "topics",
-  Gifts: "gifts",
-  Activities: "activities",
-} as const;
-
-export type SidebarPage = (typeof SidebarPage)[keyof typeof SidebarPage];
-
-export const BottomNavItem = {
-  None: "none",
-  Topics: "topics",
-  Gifts: "gifts",
-  Activities: "activities",
-} as const;
-
-export type BottomNavItem = (typeof BottomNavItem)[keyof typeof BottomNavItem];
-
 // 重新导出 State / Event 类型，保持 machine 文件的公共 API 不变
 export type { SidebarState } from "./sidebar-state";
 export { initialState } from "./sidebar-state";

src/stores/sidebar/sidebar-state.ts

@@ -1,9 +1,31 @@
 /**
  * Sidebar 状态机：State 形状 + 初始值
  *
- * SidebarPage / BottomNavItem 仍由 sidebar-machine.ts 导出（事件/上下文均需引用）。
+ * 枚举 `SidebarPage` / `BottomNavItem` 与 state 形状强相关（`currentPage` /
+ * `selectedBottomNavItem` 字段的取值集合），因此与 state 同源定义在本文件，
+ * 避免与 `sidebar-machine.ts` 形成循环引用。
  */
-import { SidebarPage, BottomNavItem } from "./sidebar-machine";
+
+/** 页面枚举（侧边栏主区域可显示的页面） */
+export const SidebarPage = {
+  DefaultView: "defaultView",
+  Profile: "profile",
+  Topics: "topics",
+  Gifts: "gifts",
+  Activities: "activities",
+} as const;
+
+export type SidebarPage = (typeof SidebarPage)[keyof typeof SidebarPage];
+
+/** 底部导航枚举（选中态） */
+export const BottomNavItem = {
+  None: "none",
+  Topics: "topics",
+  Gifts: "gifts",
+  Activities: "activities",
+} as const;
+
+export type BottomNavItem = (typeof BottomNavItem)[keyof typeof BottomNavItem];
 
 export interface SidebarState {
   currentPage: SidebarPage;