feat: implement Taqnyat SMS provider (Saudi Arabia) #18

Summary

Implement the Taqnyat SMS provider inside src/SmsBridge/Providers/Taqnyat/.

Taqnyat is a leading SMS gateway in Saudi Arabia and the wider Gulf Cooperation Council (GCC) region.

Files to create

• src/SmsBridge/Providers/Taqnyat/TaqnyatSmsProvider.cs
• src/SmsBridge/Providers/Taqnyat/TaqnyatSmsRequestMapper.cs
• src/SmsBridge/Providers/Taqnyat/TaqnyatSmsResponseMapper.cs
• src/SmsBridge/Options/TaqnyatOptions.cs
• Register UseTaqnyat() in src/SmsBridge/DependencyInjection/SmsBridgeProviderBuilder.cs
• Add HttpClientNames.Taqnyat in src/SmsBridge/Internal/Http/HttpClientNames.cs
• Add SmsProviderType.Taqnyat to the enum

Taqnyat API Details

• Endpoint: https://api.taqnyat.sa/v1/messages
• Auth: Authorization: Bearer <token>
• Request (JSON):

  {
    "recipients": ["..."],
    "body": "...",
    "sender": "..."
  }

• Response: { "statusCode": 201, "message": "...", "msgId": "..." }

Options

public sealed class TaqnyatOptions
{
    public required string BearerToken { get; init; }
    public required string From { get; init; }
}

Tests to add

• tests/SmsBridge.ProviderTests/TaqnyatResponseMapperTests.cs
• tests/SmsBridge.ProviderTests/TaqnyatProviderTests.cs

Acceptance Criteria

• Provider sends via Taqnyat REST API using IHttpClientFactory
• Response mapper checks statusCode == 201 for success
• Transient failures set IsTransientFailure = true
• UseTaqnyat() registers the provider in DI
• All tests pass — dotnet test
• dotnet build has 0 warnings