Add Serilog console logging across the API

Information at endpoint and service-method boundaries, Debug in deeper
helpers, Warning before expected/recoverable failures (not-found,
validation, agent tool errors), Error on caught exceptions. Serilog
wraps the exception handler so request-completion logs report the
resolved status code rather than the raw exception. Never logs prose
bodies or the Anthropic API key.

src/Novelly.Api/Program.cs

@@ -11,9 +11,17 @@ using Novelly.Api.Projects;
 using Novelly.Api.Questions;
 using Novelly.Api.Scenes;
 using Novelly.Api.Tags;
+using Serilog;
 
 var builder = WebApplication.CreateBuilder(args);
 
+// AddSerilog (not UseSerilog) so it becomes an additional logging provider rather than
+// replacing the one AddServiceDefaults wires up for the Aspire dashboard.
+builder.Services.AddSerilog((services, config) => config
+    .ReadFrom.Configuration(builder.Configuration)
+    .ReadFrom.Services(services)
+    .WriteTo.Console(outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {SourceContext}: {Message:lj}{NewLine}{Exception}"));
+
 builder.AddServiceDefaults();
 builder.Services.AddNovelly(builder.Configuration);
 builder.Services.AddOpenApi();
@@ -41,6 +49,11 @@ using (var scope = app.Services.CreateScope())
     await scope.ServiceProvider.GetRequiredService<NovelDbContext>().Database.MigrateAsync();
 }
 
+// Serilog's request logging wraps the exception handler (registered first = outermost)
+// so it reads the status code the handler already resolved, rather than seeing the raw
+// exception fly past and misreporting a handled 404 as a 500.
+app.UseSerilogRequestLogging();
+
 app.UseExceptionHandler(handler => handler.Run(async context =>
 {
     var exception = context.Features.Get<IExceptionHandlerFeature>()?.Error;
@@ -57,6 +70,10 @@ app.UseExceptionHandler(handler => handler.Run(async context =>
     {
         app.Logger.LogError(exception, "Unhandled exception on {Path}", context.Request.Path);
     }
+    else
+    {
+        app.Logger.LogWarning(exception, "Handled {StatusCode} on {Path}: {Title}", status, context.Request.Path, title);
+    }
 
     await Results
         .Problem(title: title, detail: exception?.Message, statusCode: status)