Fix adversarial options injection

[snapetech]

What changed

• inject IOptions<AdversarialOptions> into SecurityController
• retain the resolved value for the existing settings and statistics endpoints
• update the focused controller test and changelog

Root cause

The experimental service graph registers AdversarialOptions through the options framework, but SecurityController requested the value object directly. Dependency injection therefore supplied the constructor's optional null default, and GET /api/v0/security/adversarial returned 404 even when adversarial settings were configured.

Impact

Configured adversarial settings are now available to the security controller through the same registration used by the rest of the service graph.

Validation

dotnet test tests/slskd.Tests.Unit/slskd.Tests.Unit.csproj -c Release --filter FullyQualifiedName~SecurityControllerTests --no-restore

Result: 6 passed.