Registers Serilog via SVSim.Hosting.UseSvSimSerilog("svsim-api") right
after CreateBuilder and wraps Main in try/catch/finally so a fatal
startup exception logs before CloseAndFlush.
Also updates the SVSim.Hosting extension to gate the file sink on entry
assembly rather than the ASP.NET environment name. WebApplicationFactory
sets the environment via a hook that resolves after both CreateBuilder
and the UseSerilog callback see their environment view, so
IsEnvironment("Testing") is unreliable in tests. The entry assembly
under `dotnet test` is always "testhost", which is a reliable signal.
appsettings.json grows a Serilog section mirroring the existing
Logging:LogLevel overrides; the Logging block itself is left in place
per the spec's follow-up cleanup note.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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