feat(hrm): 添加请假统计功能

- 在控制器中新增 /stats 接口用于获取请假统计数据
- 新增 HrmLeaveStatsVo 数据传输对象定义统计结构
- 在数据访问层添加多个统计查询方法，包括按类型、部门、月份统计
- 实现服务层统计业务逻辑，包括请假汇总、分类统计、员工状态统计
- 配置 MyBatis 映射文件实现各维度统计 SQL 查询
- 添加员工总数和请假中员工数的统计功能

fad-hrm/src/main/java/com/ruoyi/hrm/mapper/HrmLeaveReqMapper.java

@@ -5,10 +5,13 @@ import com.ruoyi.common.core.mapper.BaseMapperPlus;
 import com.ruoyi.hrm.domain.HrmLeaveReq;
 import com.ruoyi.hrm.domain.bo.HrmLeaveReqBo;
 import com.ruoyi.hrm.domain.vo.HrmLeaveReqVo;
+import com.ruoyi.hrm.domain.vo.HrmLeaveStatsVo;
+import org.apache.ibatis.annotations.MapKey;
 import org.apache.ibatis.annotations.Param;
 import org.apache.ibatis.session.RowBounds;
 
 import java.util.List;
+import java.util.Map;
 
 public interface HrmLeaveReqMapper extends BaseMapperPlus<HrmLeaveReqMapper, HrmLeaveReq, HrmLeaveReqVo> {
 
@@ -17,4 +20,17 @@ public interface HrmLeaveReqMapper extends BaseMapperPlus<HrmLeaveReqMapper, Hrm
     List<HrmLeaveReqVo> selectVoWithProjectByPage(IPage<HrmLeaveReqVo> page, @Param("bo") HrmLeaveReqBo bo);
 
     List<HrmLeaveReqVo> selectVoWithProjectList(@Param("bo") HrmLeaveReqBo bo);
+
+    // 统计相关方法
+    Map<String, Object> selectLeaveSummary();
+
+    List<Map<String, Object>> selectLeaveByType();
+
+    List<Map<String, Object>> selectLeaveByDept();
+
+    List<Map<String, Object>> selectLeaveByMonth(@Param("year") Integer year);
+
+    Integer selectTotalEmployees();
+
+    Integer selectLeavingEmployees();
 }