fix: 修复部署问题

- 修复 RootController 返回 index.html
- 修复 MyBatis 缓存配置
- 修复 session scope bean 注入问题

src/main/java/com/example/scaffold/mapper/UserMapper.java

@@ -2,7 +2,7 @@ package com.example.scaffold.mapper;
 
 import com.example.scaffold.entity.User;
 import org.apache.ibatis.annotations.*;
-import org.apache.ibatis.cache.decorators.LruCache;
+import org.apache.ibatis.cache.impl.PerpetualCache;
 
 import java.util.List;
 
@@ -17,7 +17,7 @@ import java.util.List;
  * 5. @CacheNamespace - 二级缓存
  */
 @Mapper
-@CacheNamespace(implementation = LruCache.class, size = 1024)
+@CacheNamespace
 public interface UserMapper {
     
     /**