feat: 将 AuthModalProvider 迁移到 Redux

## 主要改动

### 新增
- 创建 `store/slices/authModalSlice.js` - Redux Slice 管理认证弹窗状态
- 创建 `hooks/useAuthModal.js` - 自定义 Hook，组合 Redux 状态和业务逻辑

### 修改
- 更新 `store/index.js` - 添加 authModal reducer
- 更新 `App.js` - 移除 AuthModalProvider 包裹层
- 更新 5 个组件的 import 路径：
  - AuthFormContent.js
  - AuthModalManager.js
  - WechatRegister.js
  - HomeNavbar.js
  - ProtectedRoute.js

### 删除
- 删除 `contexts/AuthModalContext.js` - 旧的 Context 实现

## 迁移效果

- ✅ 减少 Provider 嵌套层级（4层 → 3层）
- ✅ 统一状态管理架构（Redux）
- ✅ 更好的调试体验（Redux DevTools）
- ✅ 保持 API 兼容性（无破坏性修改）

## 技术细节

- 使用 `useRef` 存储 `onSuccessCallback`（函数不可序列化）
- 保持与 AuthContext 的依赖关系（AuthProvider 暂未迁移）
- 所有业务逻辑保持不变，仅改变状态管理方式

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/components/Auth/AuthFormContent.js

@@ -29,7 +29,7 @@ import {
 } from "@chakra-ui/react";
 import { FaLock, FaWeixin } from "react-icons/fa";
 import { useAuth } from "../../contexts/AuthContext";
-import { useAuthModal } from "../../contexts/AuthModalContext";
+import { useAuthModal } from "../../hooks/useAuthModal";
 import { useNotification } from "../../contexts/NotificationContext";
 import { authService } from "../../services/authService";
 import AuthHeader from './AuthHeader';

src/components/Auth/AuthModalManager.js

@@ -8,7 +8,7 @@ import {
   ModalCloseButton,
   useBreakpointValue
 } from '@chakra-ui/react';
-import { useAuthModal } from '../../contexts/AuthModalContext';
+import { useAuthModal } from '../../hooks/useAuthModal';
 import AuthFormContent from './AuthFormContent';
 
 /**

src/components/Auth/WechatRegister.js

@@ -15,7 +15,7 @@ import { FaQrcode } from "react-icons/fa";
 import { FiAlertCircle } from "react-icons/fi";
 import { useNavigate } from "react-router-dom";
 import { authService, WECHAT_STATUS, STATUS_MESSAGES } from "../../services/authService";
-import { useAuthModal } from "../../contexts/AuthModalContext";
+import { useAuthModal } from "../../hooks/useAuthModal";
 import { useAuth } from "../../contexts/AuthContext";
 import { logger } from "../../utils/logger";
 import { useAuthEvents } from "../../hooks/useAuthEvents";