feat(todo): 新增多人待办清单后端

- 新增 t_todo 表（user_id 隔离 + 逻辑删除），增量脚本 sql/delta_todo.sql
- entity/mapper/service/controller 四层，复用 MyBatis-Plus 与 Result
- /todo/** 纳入 JWT 认证，user_id 一律由 token 解析，禁止前端传入

src/main/java/com/freedom/admin/service/TodoService.java

@@ -0,0 +1,13 @@
+package com.freedom.admin.service;
+
+import com.baomidou.mybatisplus.extension.service.IService;
+import com.freedom.admin.entity.Todo;
+
+/**
+ * 业务层-待办清单表
+ *
+ * @author zhangjiaxun
+ */
+public interface TodoService extends IService<Todo> {
+
+}

src/main/java/com/freedom/admin/service/impl/TodoServiceImpl.java

@@ -0,0 +1,19 @@
+package com.freedom.admin.service.impl;
+
+import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
+import com.freedom.admin.entity.Todo;
+import com.freedom.admin.mapper.TodoMapper;
+import com.freedom.admin.service.TodoService;
+import lombok.extern.log4j.Log4j2;
+import org.springframework.stereotype.Service;
+
+/**
+ * 业务层实现-待办清单表
+ *
+ * @author zhangjiaxun
+ */
+@Service
+@Log4j2
+public class TodoServiceImpl extends ServiceImpl<TodoMapper, Todo> implements TodoService {
+
+}