fix: 实验步骤表结构修改

sql/demo.sql

@@ -161,7 +161,8 @@ CREATE TABLE IF NOT EXISTS logs (
 CREATE TABLE IF NOT EXISTS task_steps (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
     task_id INTEGER,
-    step_description TEXT
+    step_description TEXT,
+    create_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 );
 
 -- 创建 Functions 功能记录表