Move the federation code under Federation/, namespaces only

Services/Federation and Controllers/ServerToServer become
Federation/{Actors,Signing,Inbox,Outbox,Rendering,Controllers}, the first step
of the roadmap's layout. No type, route or behaviour changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Federation/Controllers/UsersController.cs

@@ -0,0 +1,12 @@
+using Microsoft.AspNetCore.Mvc;
+
+namespace PrivaPub.Federation.Controllers
+{
+	[ApiController, Route("users")]
+	public class UsersController : ControllerBase
+	{
+		[HttpGet, Route("{actor}")]
+		public IActionResult GetActor(string actor) =>
+			RedirectPermanent($"/peasants/{Uri.EscapeDataString(actor)}");
+	}
+}