Let a session's transport say what it negotiated

ISshConnection and ISftpSession both carry Cipher now — the server-to-client
algorithm off SSH.NET's own ConnectionInfo, captured once because a rekey is
not an event that library raises — and TerminalWorkspace.GetSessionFacts hands
that plus the host key's algorithm back per session, without ever handing over
the connection itself. Nothing reads either yet; the status bar that will is
the next commit.

tests/DodoSSH.Client.Ssh.Tests/KeyAuthenticationTests.cs

@@ -36,6 +36,12 @@ public sealed class KeyAuthenticationTests(SshServerFixture fixture)
 
         connection.IsConnected.ShouldBeTrue();
 
+        // The one place this suite checks Cipher against a real handshake rather than a fake's fixed string.
+        // SSH.NET negotiates whatever the container's sshd offers first from its own preference list, so the
+        // exact algorithm is not pinned here — only that ConnectionInfo.CurrentServerEncryption came back as
+        // something rather than the empty string a stalled or pre-handshake read would produce.
+        connection.Cipher.ShouldNotBeNullOrEmpty();
+
         // Authenticated is not the same as usable: a channel has to open on the connection too.
         await using var shell = await connection.OpenShellAsync(TerminalSize.Default, Token);