Remove unsafe Json.NET type metadata from transaction request serialization

[Copilot]

TransactionService was serializing outbound request DTOs with TypeNameHandling.All, which causes Json.NET to emit $type metadata and is unsafe in security-sensitive paths. This change removes that behavior from the mobile transaction request pipeline and adds coverage to prevent it from reappearing.

• Serialization change

  • Replaced the explicit JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All } usage in TransactionService.SendTransactionRequest(...) with standard Json.NET serialization.
  • This keeps the request payload as plain JSON for the concrete DTOs already used by the service.

• Regression coverage

  • Added a focused TransactionService test that captures the outbound logon request payload and verifies:
    • no $type metadata is emitted
    • expected request fields are still serialized

• Result

  • Outgoing transaction requests no longer include polymorphic type metadata.
  • Existing request shape is preserved for the concrete request models used by the service.

// Before
String requestSerialised = JsonConvert.SerializeObject(
    request,
    new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All });

// After
String requestSerialised = JsonConvert.SerializeObject(request);

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.25.1/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /opt/hostedtoolcache/CodeQL/2.25.1/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[codacy-production]

Up to standards ✅

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