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.App.Tests/FakeSsh.cs

@@ -83,6 +83,9 @@ internal sealed class FakeSftpSession(SshConnectionRequest request) : ISftpSessi
     public HostKeyPresentation HostKey { get; } =
         new(request.Host, request.Port, "ssh-ed25519", "SHA256:fake");
 
+    /// <inheritdoc />
+    public string Cipher { get; } = "aes256-gcm@openssh.com";
+
     /// <inheritdoc />
     public string HomeDirectory => $"/home/{request.Username}";
 
@@ -139,6 +142,9 @@ internal sealed class FakeSshConnection(SshConnectionRequest request) : ISshConn
     public HostKeyPresentation HostKey { get; } =
         new(request.Host, request.Port, "ssh-ed25519", "SHA256:fake");
 
+    /// <inheritdoc />
+    public string Cipher { get; } = "aes256-gcm@openssh.com";
+
     /// <inheritdoc />
     public Task<ISshShellSession> OpenShellAsync(
         TerminalSize size,