🐛 fix(CreateDatabase): 修复 Oracle 新建数据库时因缺少 Service Name 报错

- 前端 Oracle/达梦连接保留原始 database 字段而非清空
- 后端添加 Oracle/达梦不支持此入口创建的友好提示
- refs #223

frontend/src/components/Sidebar.tsx

@@ -2189,7 +2189,7 @@ const Sidebar: React.FC<{ onEditConnection?: (conn: SavedConnection) => void }>
               ...conn.config, 
               port: Number(conn.config.port),
               password: conn.config.password || "",
-              database: "", // No db selected
+              database: (conn.config.type === 'oracle' || conn.config.type === 'dameng') ? (conn.config.database || "") : "",
               useSSH: conn.config.useSSH || false,
               ssh: conn.config.ssh || { host: "", port: 22, user: "", password: "", keyPath: "" }
           };

internal/app/methods_db.go

@@ -109,6 +109,8 @@ func (a *App) CreateDatabase(config connection.ConnectionConfig, dbName string)
 		// MariaDB uses same syntax as MySQL
 	} else if dbType == "sphinx" {
 		return connection.QueryResult{Success: false, Message: "Sphinx 暂不支持创建数据库"}
+	} else if dbType == "oracle" || dbType == "dameng" {
+		return connection.QueryResult{Success: false, Message: fmt.Sprintf("当前数据源（%s）的「数据库」实际为用户/Schema，暂不支持通过此入口创建，请使用 SQL 编辑器执行 CREATE USER 语句", dbType)}
 	}
 
 	_, err = dbInst.Exec(query)