Add configurable path base for API routing

src/MemberCenter.Api/Program.cs

@@ -128,8 +128,15 @@ builder.Services.AddHttpClient<SendEngineWebhookPublisher>();
 builder.Services.AddScoped<ISendEngineWebhookPublisher, SendEngineWebhookPublisher>();
 
 var app = builder.Build();
+var pathBase = builder.Configuration["PathBase"];
 
 app.UseForwardedHeaders();
+if (!string.IsNullOrWhiteSpace(pathBase))
+{
+    var normalizedPathBase = pathBase.StartsWith('/') ? pathBase : $"/{pathBase}";
+    app.UsePathBase(normalizedPathBase);
+}
+
 app.UseRouting();
 app.UseAuthentication();
 app.UseAuthorization();