Moves carry follows over; first DMs to Lemmy 0.19 and Mbin go as ChatMessage

Two owner decisions of 2026-10-05, both recorded in ROADMAP:
- After a verified Move the personas following the old account follow the new one, in the same lists, and a mute or
  block of the old account carries over, as Mastodon does it.
- A direct message to one account on a server whose NodeInfo names Lemmy before 1.0 or Mbin goes as a ChatMessage,
  the one place PrivaPub decides by a server's software (invariant 17). G-0008 is closed.

Mbin addresses its private messages to the recipient's profile page, so a Create addressed to a persona's /@name now
reaches the persona. Checked live: moves 8/8, Lemmy 0.19 30/30, Mbin 26/26 with messages both ways. The software
theory runs alone, since every test's peer shares 127.0.0.1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub.Tests/Domain/ContentRendererTests.cs

@@ -68,6 +68,7 @@ namespace PrivaPub.Tests.Domain
 
 			public Task<LocalActor> FindById(LocalActorKind kind, string id, CancellationToken token) => throw new NotSupportedException();
 			public Task<LocalActor> FindByUri(string actorUri, CancellationToken token) => throw new NotSupportedException();
+			public Task<LocalActor> FindByAddress(string address, CancellationToken token) => throw new NotSupportedException();
 			public Task<LocalActor> GetInstanceActor(CancellationToken token) => throw new NotSupportedException();
 			public Task<bool> IsUserNameTaken(string userName, CancellationToken token) => throw new NotSupportedException();
 			public Task<bool> TryReserveUserName(string userName, LocalActorKind kind, string ownerId, CancellationToken token) => throw new NotSupportedException();