Add the digital interface, running MMTTY under Wine

MMTTY and 2Tone have no socket or pipe interface: N1MM hosts XMMT.ocx and
exchanges window messages with the engine. A Linux process cannot load that
control, so bridge/nonemm-mmtty-bridge.exe hosts it under Wine and passes
lines over its standard input and output. docs/digital-bridge.md states the
protocol and what the control needs.

The window is N1MM's: receive pane with coloured callsigns, grab list, call
stacking, twenty-four macro buttons and the engine controls. One left click
copies what is under it — a callsign to the callsign box, anything else to the
exchange box the contest keeps for that kind of value.

Config > Digital registers XMMT.ocx in the Wine prefix on its own, making the
prefix first if it is not there. The engine, the bridge and the control start
at the copies shipped beside the program.

The bridge reads the control's own events. OnTranslateMessage carries only the
messages the control has no event for, so nothing was ever decoded through it.

hamlib's data mode names read as digital modes now, and a mode typed into the
callsign box changes mode the way a frequency changes band, so a station with
no radio can reach RTTY at all.

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

tests/Nonemm.Digital.Tests/FakeBridge.cs

@@ -0,0 +1,54 @@
+using Nonemm.Digital;
+
+namespace Nonemm.Digital.Tests;
+
+/// A bridge that goes nowhere: the test reads what was sent to it and says what
+/// comes back.
+public sealed class FakeBridge : BridgeChannel
+{
+    private readonly List<string> sent = [];
+
+    public bool IsStarted { get; private set; }
+
+    public IReadOnlyList<string> Sent
+    {
+        get
+        {
+            lock (sent)
+            {
+                return sent.ToArray();
+            }
+        }
+    }
+
+    public event EventHandler<string>? LineReceived;
+
+    public event EventHandler<string>? Failed;
+
+    public Task StartAsync(CancellationToken cancellation = default)
+    {
+        IsStarted = true;
+        return Task.CompletedTask;
+    }
+
+    public Task SendAsync(string line, CancellationToken cancellation = default)
+    {
+        lock (sent)
+        {
+            sent.Add(line);
+        }
+        return Task.CompletedTask;
+    }
+
+    public Task<string> ToWindowsPathAsync(string path, CancellationToken cancellation = default) =>
+        Task.FromResult("Z:" + path.Replace('/', '\\'));
+
+    public void Say(string verb, params string[] fields) =>
+        LineReceived?.Invoke(this, BridgeLine.Write(verb, fields));
+
+    public void Stop(string why) => Failed?.Invoke(this, why);
+
+    public void Dispose()
+    {
+    }
+}