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.

src/DodoSSH.Client.Ssh/SshNetConnectionFactory.cs

@@ -274,6 +274,16 @@ internal sealed class SshNetConnection(SshClient client, HostKeyPresentation hos
     /// <inheritdoc />
     public HostKeyPresentation HostKey { get; } = hostKey;
 
+    /// <inheritdoc />
+    /// <remarks>
+    /// Read at construction rather than lazily: by the time an <see cref="SshNetConnection"/> exists,
+    /// <see cref="SshNetConnectionFactory.ConnectAsync"/> has already awaited <c>client.ConnectAsync</c>, so
+    /// <c>ConnectionInfo</c> is already populated and there is no earlier moment reading it would race. SSH.NET
+    /// types the property as a non-nullable <c>string</c>, so this reads straight through rather than coalescing
+    /// a null that the library's own contract says cannot occur.
+    /// </remarks>
+    public string Cipher { get; } = client.ConnectionInfo.CurrentServerEncryption;
+
     /// <inheritdoc />
     public Task<ISshShellSession> OpenShellAsync(TerminalSize size, CancellationToken cancellationToken)
     {