Add DeepDrftCms RCL skeleton, mount at /cms, switch NetBlocks to NuGet

DeepDrftCms/CmsStartup.cs

@@ -0,0 +1,12 @@
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DeepDrftCms;
+
+public static class CmsStartup
+{
+    public static IServiceCollection AddCmsServices(this IServiceCollection services)
+    {
+        // CMS-specific services registered here as implementation waves land.
+        return services;
+    }
+}