feat: project skeleton + DB migrations V1-V12 + ga-common framework

- Gradle multi-module: ga-common, ga-core, ga-api, ga-batch, ga-admin
- Flyway V1-V12: org/product/rule/receive/ledger/settle/batch/code/menu/system + seed
- ga-common (complete):
  - model: ApiResponse, PageResponse, SearchParam, TreeNode
  - exception: ErrorCode, BizException, GlobalExceptionHandler
  - annotation + aop: @RequirePermission, @DataChangeLog, ApiLog
  - auth + security: JWT, SecurityConfig
  - mybatis: BaseMapper, EncryptTypeHandler, JsonTypeHandler, AuditInterceptor
  - code (Redis cached) / menu (RBAC tree) / file / system / notification
  - excel: SXSSF+Cursor export, SAX+batch import (1M/700K rows)
  - util: Date/Money/Mask/Encrypt/Security

ga-common/src/main/java/com/ga/common/notification/NotificationMapper.java

@@ -0,0 +1,17 @@
+package com.ga.common.notification;
+
+import org.apache.ibatis.annotations.Mapper;
+import org.apache.ibatis.annotations.Param;
+
+import java.util.List;
+
+@Mapper
+public interface NotificationMapper {
+    int insert(NotificationVO vo);
+    int insertBatch(@Param("list") List<NotificationVO> list);
+    List<NotificationVO> selectByUser(@Param("userId") Long userId);
+    int countUnread(@Param("userId") Long userId);
+    int markRead(@Param("notiId") Long notiId, @Param("userId") Long userId);
+    int markAllRead(@Param("userId") Long userId);
+    int deleteOld(@Param("days") int days);
+}