feat: 集成Flyway数据库迁移工具

- 添加Flyway依赖到pom.xml
- 配置application.yml启用Flyway
- 创建迁移脚本目录db/migration
- 添加V1基线脚本和V2项目字段迁移脚本
- 添加DATABASE_MIGRATION.md使用文档

pom.xml

@@ -228,6 +228,16 @@
             <artifactId>lombok</artifactId>
             <scope>provided</scope>
         </dependency>
+
+        <!-- Flyway 数据库迁移 -->
+        <dependency>
+            <groupId>org.flywaydb</groupId>
+            <artifactId>flyway-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.flywaydb</groupId>
+            <artifactId>flyway-mysql</artifactId>
+        </dependency>
     </dependencies>
 
     <build>