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

src/Nonemm.Digital/BridgeChannel.cs

@@ -0,0 +1,20 @@
+namespace Nonemm.Digital;
+
+/// The line connection to a bridge process. What is behind it is Wine in
+/// production and a fake in the tests.
+public interface BridgeChannel : IDisposable
+{
+    /// A line the bridge wrote. Raised on the reader thread.
+    event EventHandler<string>? LineReceived;
+
+    /// The bridge stopped on its own. The text says what is known about why.
+    event EventHandler<string>? Failed;
+
+    Task StartAsync(CancellationToken cancellation = default);
+
+    Task SendAsync(string line, CancellationToken cancellation = default);
+
+    /// The path as the engine sees it. Wine has its own drive letters, and the
+    /// engine is started by name from a Windows command line.
+    Task<string> ToWindowsPathAsync(string path, CancellationToken cancellation = default);
+}