feat: 任务列表显示 turn_id 与 root_turn_id

host.py dispatch 打印补 turn_id/root_turn_id；执行器解析（local/Docker）透传；worker 写回 tasks 新列（新值非空才覆盖）；server 迁移与接口字段；控制台任务列表新增 turn/root turn 两列（短显+悬停全文）；新单测 9 个。

cloud/db.py

@@ -839,6 +839,8 @@ POSTGRES_SCHEMA = (
     "forked_from TEXT, "
     "environment_id TEXT, "
     "resume_message TEXT, "
+    "turn_id TEXT, "
+    "root_turn_id TEXT, "
     "UNIQUE(project_id, idempotency_key))",
     "CREATE INDEX IF NOT EXISTS idx_tasks_status ON tasks(status)",
     # 附件包与任务附件：与 server._ensure_uploads_tables 同款，