fix: creating a room failed with a blank "Failed to copy room"

The 2023 client sends rooms/{id}/clone through the same RecNet rooms
helper as "save room" and "restore subroom save", which reads the
{success, value, error} envelope. The clone handler answered with the
bare room details, so the client found no success flag and rejected the
reply with an empty error, even though the room had been created.

Clone now returns the envelope with the full room details in value, and
refusals (unknown source, cloning not allowed) are a 200 with
success=false and a message instead of a bodyless 404/403.

DorkNet.Server.Tests/PrivateRoomInstanceTests.cs

@@ -42,7 +42,7 @@ public sealed class PrivateRoomInstanceTests : IClassFixture<DorkNetServerFactor
         var text = await resp.Content.ReadAsStringAsync();
         Assert.True(resp.IsSuccessStatusCode, $"{(int)resp.StatusCode}: {text}");
         using var json = JsonDocument.Parse(text);
-        var cloneId = json.RootElement.GetProperty("RoomId").GetInt64();
+        var cloneId = json.RootElement.GetProperty("value").GetProperty("RoomId").GetInt64();
 
         await using var scope = _factory.Services.CreateAsyncScope();
         var db = scope.ServiceProvider.GetRequiredService<DorkNetDbContext>();