feat(bff): placeholder BFF + /health endpoint (closes #28) (#34)

services/bff/Bff.Api/Program.cs

@@ -0,0 +1,12 @@
+var builder = WebApplication.CreateBuilder(args);
+builder.Services.AddHealthChecks();
+
+var app = builder.Build();
+
+app.MapGet("/", () => "BFF placeholder");
+app.MapHealthChecks("/health");
+
+app.Run();
+
+// Exposed so the test host (WebApplicationFactory<Program>) can boot the app.
+public partial class Program;