feat: implement D7 Networks SMS provider (UAE / Global) #20

Summary

Implement the D7 Networks SMS provider inside src/SmsBridge/Providers/D7Networks/.

D7 Networks (Direct7 Networks) is a UAE-based global messaging platform with strong reach in the Middle East, Asia, and Africa.

Files to create

• src/SmsBridge/Providers/D7Networks/D7NetworksSmsProvider.cs
• src/SmsBridge/Providers/D7Networks/D7NetworksSmsRequestMapper.cs
• src/SmsBridge/Providers/D7Networks/D7NetworksSmsResponseMapper.cs
• src/SmsBridge/Options/D7NetworksOptions.cs
• Register UseD7Networks() in src/SmsBridge/DependencyInjection/SmsBridgeProviderBuilder.cs
• Add HttpClientNames.D7Networks in src/SmsBridge/Internal/Http/HttpClientNames.cs
• Add SmsProviderType.D7Networks to the enum

D7 Networks API Details

• Endpoint: https://api.d7networks.com/messages/v1/send
• Auth: Authorization: Bearer <api_token>
• Request (JSON):

  {
    "messages": [{
      "channel": "sms",
      "recipients": ["..."],
      "content": "...",
      "msg_type": "text",
      "data_coding": "text"
    }],
    "message_globals": { "originator": "..." }
  }

• Response: { "request_id": "...", "status": "pending" }

Options

public sealed class D7NetworksOptions
{
    public required string ApiToken { get; init; }
    public required string From { get; init; }
}

Tests to add

• tests/SmsBridge.ProviderTests/D7NetworksResponseMapperTests.cs
• tests/SmsBridge.ProviderTests/D7NetworksProviderTests.cs

Acceptance Criteria

• Provider sends via D7 Networks REST API using IHttpClientFactory
• Response mapper maps request_id and status to SmsSendResult
• Transient failures set IsTransientFailure = true
• UseD7Networks() registers the provider in DI
• All tests pass — dotnet test
• dotnet build has 0 warnings