feat: implement Sendchamp SMS provider (Nigeria) #55

Summary

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

Sendchamp is a Nigeria-based communication API provider with SMS, WhatsApp, email, and voice APIs. This fills an additional Nigerian provider gap beyond Termii, SmartSMSSolutions, BulkSMSNigeria, and MultiTexter.

Official docs:

• Developer portal: https://developers.sendchamp.com/
• Guides: https://docs.sendchamp.com
• API reference: https://sendchamp.readme.io/reference

Files to create

• src/SmsBridge/Providers/Sendchamp/SendchampSmsProvider.cs
• src/SmsBridge/Providers/Sendchamp/SendchampSmsRequestMapper.cs
• src/SmsBridge/Providers/Sendchamp/SendchampSmsResponseMapper.cs
• src/SmsBridge/Options/SendchampOptions.cs
• Register UseSendchamp() in src/SmsBridge/DependencyInjection/SmsBridgeProviderBuilder.cs
• Add HttpClientNames.Sendchamp in src/SmsBridge/Internal/Http/HttpClientNames.cs
• Add SmsProviderType.Sendchamp to the enum

Sendchamp API Details

• API docs are hosted through Sendchamp ReadMe and GitBook.
• Auth uses an API key/token in the request headers.
• SMS sending supports sender, recipient, and message body fields.
• Confirm the current base URL and send endpoint from the ReadMe API reference during implementation.

Options

public sealed class SendchampOptions
{
    public required string ApiKey { get; init; }
    public required string Sender { get; init; }
}

Implementation Notes

• Re-check the current Sendchamp SMS endpoint immediately before implementation because the API reference is hosted in a dynamic ReadMe site.
• Keep Sendchamp isolated from other Nigerian providers; do not reuse Termii request/response models.
• Avoid logging the API key or raw authorization header.
• Map provider message id/reference fields to SmsSendResult.ProviderMessageId.

Tests to add

• tests/SmsBridge.ProviderTests/SendchampResponseMapperTests.cs
• tests/SmsBridge.ProviderTests/SendchampProviderTests.cs

Acceptance Criteria

• Provider sends SMS using Sendchamp's current SMS API endpoint and IHttpClientFactory
• Provider authenticates with configured API key/token
• Request mapper emits sender, recipient, and message body
• Response mapper maps provider message id/reference to SmsSendResult.ProviderMessageId
• Provider maps Sendchamp errors to failed SmsSendResult
• Transient HTTP failures set IsTransientFailure = true
• UseSendchamp() registers the provider in DI
• All tests pass - dotnet test
• dotnet build has 0 warnings