Show what has gone out in the transmit pane

The transmit pane is now the type-ahead buffer. What has gone to the engine is
in red beside the box and cannot be reached; what is still to go is in the box
and can be typed over, added to or deleted while the engine works through it.
A macro fills the pane rather than the engine, so the operator can correct a
call the message is still sending.

The cursor holds the pump: nothing behind it goes out, so an engine that
catches up with the operator idles instead of transmitting half a word. With
the box out of focus there is no cursor and everything goes.

Escape and the RX button drop what has not gone out and stop the engine where
it is. Enter puts in the carriage return the engine takes as a new line. The
pane starts empty for the next message.

The baud rate the pump counts by is in the digital setup window, beside the
alignment frequency. It has to match the engine: 45.45 unless the contest says
otherwise.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

src/Nonemm.App/AppSession.cs

@@ -132,7 +132,7 @@ public sealed class AppSession : IDisposable
     public MmttyEngine? Digital => digital;
 
     /// The same engine as something a macro can be sent through.
-    public MessageSender? DigitalKeyer => digitalSender;
+    public DigitalEngineSender? DigitalKeyer => digitalSender;
 
     /// Alternating CQ, or null while there is no keyer. It needs two radios to
     /// do anything, and a keyer that reports when a message has gone out.
@@ -333,7 +333,7 @@ public sealed class AppSession : IDisposable
         MmttyEngine started = new(channel, options);
         await started.StartAsync();
         digital = started;
-        digitalSender = new DigitalEngineSender(started);
+        digitalSender = new DigitalEngineSender(started, Settings.DigitalBaud);
         Changed?.Invoke(this, EventArgs.Empty);
         return started;
     }