fix(database): enforce Flyway migration governance

xiaoqu-agent-service/sql/rollback/V1__init.down.sql

@@ -0,0 +1,8 @@
+-- 仅用于尚未承载业务数据的环境，按依赖逆序删除整个服务自有结构。
+DROP TABLE IF EXISTS admin_user;
+DROP TABLE IF EXISTS audit_log;
+DROP TABLE IF EXISTS token_scope;
+DROP TABLE IF EXISTS scope_tool;
+DROP TABLE IF EXISTS tool;
+DROP TABLE IF EXISTS agent_scope;
+DROP TABLE IF EXISTS agent_api_key;

xiaoqu-agent-service/sql/rollback/V2__p4_admin.down.sql

@@ -0,0 +1,15 @@
+-- PBKDF2 哈希长度超过 64 时拒绝回退，避免截断管理员密码。
+DELIMITER //
+CREATE PROCEDURE rollback_v2_p4_admin()
+BEGIN
+    IF EXISTS (SELECT 1 FROM admin_user WHERE CHAR_LENGTH(password_hash) > 64) THEN
+        SIGNAL SQLSTATE '45000'
+            SET MESSAGE_TEXT = 'V2 rollback blocked: PBKDF2 password hashes already exist';
+    END IF;
+    ALTER TABLE admin_user
+        MODIFY COLUMN password_hash CHAR(64) NOT NULL COMMENT '密码 SHA-256 hex';
+END //
+DELIMITER ;
+
+CALL rollback_v2_p4_admin();
+DROP PROCEDURE rollback_v2_p4_admin;