serial: pipe:vrio named-pipe transport, no com0com needed

NamedPipeTransport connects as a client to vRIO's \\.\pipe\vrio (the
DOSBox-X fork's role) and speaks the shared typed-frame contract
(PipeFraming: 0x00 data / 0x01 modem lines, null-modem crossed). The COM
path's DTR reset pulse is replayed in-band on connect. Peer disconnects
and framing violations surface as the 0-byte transport-closed read the
link already understands.

RioTransportFactory routes endpoint strings — pipe:name (vRIO's own
picker syntax) to the pipe transport, everything else to
SerialPortTransport — and is wired into RioCoordinator and all three
RioSerialMonitor modes, so profiles (RioComPort/DefaultRioComPort) and
the bench tools take pipe endpoints anywhere a COM name went.

Gotcha baked into the design: named pipes here have 0-byte buffers, so a
write blocks until the peer reads it, and vRIO also writes its lines
frame before reading — the on-connect pulse frames are therefore queued
as overlapped writes (pipe writes drain in issue order, preserving the
edge positions) instead of blocking the constructor into a mutual
write-first deadlock.

Verified end-to-end against the real VRioDevice + VRioPipeService over
\\.\pipe\vrio: version 4.2 + check replies, 137 analog polls, lamp
commands ACKed, zero framing errors. 322 tests green, both flavors.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/RioJoy.Core/Profiles/AppConfig.cs

@@ -7,7 +7,11 @@ namespace RioJoy.Core.Profiles;
 /// </summary>
 public sealed class AppConfig
 {
-    /// <summary>Default RIO COM port when a profile doesn't specify one.</summary>
+    /// <summary>
+    /// Default RIO endpoint when a profile doesn't specify one: a COM port
+    /// name ("COM1"), or "pipe:vrio" to reach the vRIO emulator over its
+    /// named pipe (no com0com pair; see RioTransportFactory).
+    /// </summary>
     public string DefaultRioComPort { get; set; } = "COM1";
 
     /// <summary>

src/RioJoy.Core/Profiles/RioProfile.cs

@@ -15,7 +15,7 @@ public sealed class RioProfile
     /// <summary>Display name (unique within a library).</summary>
     public string Name { get; set; } = "Unnamed";
 
-    /// <summary>RIO serial port (e.g. "COM3"); null = use the app default.</summary>
+    /// <summary>RIO endpoint ("COM3", or "pipe:vrio" for the emulator); null = use the app default.</summary>
     public string? RioComPort { get; set; }
 
     /// <summary>Plasma/VFD serial port; null = use the app default or none.</summary>