Replace Console.Error.WriteLine with WriteLineAsync in Program.cs

## What version of FlowSynx?
> 1.2.1

## Describe the bug
Currently, error messages in the `Program.cs` are written using synchronous Console.Error.WriteLine, line 115:

```csharp
Console.Error.WriteLine(ex.Message);
```

### Proposed Change:
- Replace synchronous calls with the asynchronous version:

```csharp
await Console.Error.WriteLineAsync(ex.Message);
```