🐛 fix(oceanbase): 修复 Oracle 租户跳板机连接预探测失败

- 修复 OceanBase Oracle 预探测未走 SSH 隧道导致内网 IP 被本机直连误判不可达的问题
- 预探测阶段复用完整连接配置，支持通过 SSH 跳板机访问目标地址
- 区分本机 TCP 不可达与 SSH 跳板机访问失败，优化错误提示
- 保留 OBClient 与 TNS 双路径路由逻辑，避免协议判断回退
- 补充 OceanBase Oracle SSH 预探测与网络失败回归测试

internal/ssh/ssh.go

@@ -116,6 +116,22 @@ func RegisterSSHNetwork(sshConfig connection.SSHConfig) (string, error) {
 	return netName, nil
 }
 
+// DialContextThroughSSH creates a context-aware connection through an SSH tunnel.
+func DialContextThroughSSH(ctx context.Context, config connection.SSHConfig, network, address string) (net.Conn, error) {
+	client, err := GetOrCreateSSHClient(config)
+	if err != nil {
+		return nil, fmt.Errorf("建立 SSH 连接失败：%w", err)
+	}
+
+	conn, err := dialContext(ctx, client, network, address)
+	if err != nil {
+		return nil, fmt.Errorf("通过 SSH 隧道连接到 %s 失败：%w", address, err)
+	}
+
+	logger.Infof("已通过 SSH 隧道连接到：%s", address)
+	return conn, nil
+}
+
 // sshClientCache stores SSH clients to avoid creating multiple connections
 var (
 	sshClientCache   = make(map[sshClientCacheKey]*ssh.Client)