feat: 实现邮箱验证码和邮箱绑定功能

- 添加邮件发送服务实现(EmailService/EmailServiceImpl)
- 新增发送验证码、绑定邮箱、解绑邮箱接口
- 用户实体新增邮箱相关字段(userEmail/userEmailVerified)
- 添加邮件配置和JavaMailSender Bean
- 放行邮箱验证码接口(/v1/user/email/send-code)
- 新增ContextHolderUtils工具类用于获取当前用户上下文
- 完善Swagger文档注解

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

.idea/CoolRequestCommonStatePersistent.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="CoolRequestCommonStatePersistent">
-    <option name="searchCache" value="UserRegisterRequestDTO" />
+    <option name="searchCache" value="JwtAuthenticationFilter" />
   </component>
 </project>