迁移：将DB变更记录SQL文件移动到sql目录下

sql/迁移记录-DB变更记录/202509031300alter_table_doc_statistics_definiton.sql

@@ -0,0 +1,8 @@
+   ALTER TABLE "doc_statistics_definition"
+  ADD COLUMN "unit" varchar(50) COLLATE "pg_catalog"."default" DEFAULT ''::character varying;
+   COMMENT ON COLUMN "doc_statistics_definition"."unit" IS '统计值单位（如“次”“mg”“分钟”等）';
+   
+   -- 插入文档统计表格结构修改的迁移记录
+INSERT INTO __MigrationsHistory (MigrationId, ProductVersion)
+VALUES ('202509031300alter_table_doc_statistics_definiton', '1.0.0');
+