✨ feat: 美化登录界面并集成登录模态框

- 重设计未登录状态UI，添加动画效果和渐变按钮
- 集成LoginModal组件，提供完整的登录体验
- 新增游客浏览功能，提升用户体验
- 切换至测试环境API (api-test.mixvideo.bowong.cc)
- 添加@expo/vector-icons图标库依赖

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

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

lib/api/client.ts

@@ -1,7 +1,7 @@
 import { fetch, FetchRequestInit } from 'expo/fetch';
 import { storage } from '../storage';
 
-const BASE_URL = 'https://api.mixvideo.bowong.cc';
+const BASE_URL = 'https://api-test.mixvideo.bowong.cc';
 
 export interface ApiRequestOptions extends FetchRequestInit {
   params?: Record<string, string | number | boolean | undefined>;