Pipe endpoints join the connection pickers; no more COM11/COM12 auto-bind

Each device row now serves one endpoint at a time, picked from a list of
pipe:vrio / pipe:vplasma (first, default) plus the machine's COM ports —
nothing opens automatically at startup. The pipe services gained an
IsListening property and are started/stopped by the row's Open/Close
button instead of running for the whole app lifetime, which also retires
the dual-transport warning. Status line shows the active endpoint;
OFFLINE when none. Standalone vPLASMA is unchanged (hardwired COM12 +
permanent pipe). Also fixes the xUnit1031 warnings in the plasma pipe
tests.

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

src/VRio.Core/Device/VRioPipeService.cs

@@ -67,6 +67,9 @@ public sealed class VRioPipeService : IDisposable
     /// <summary>The served pipe name (without the <c>\\.\pipe\</c> prefix).</summary>
     public string PipeName => _pipeName;
 
+    /// <summary>True while the server is up (whether or not a client is connected).</summary>
+    public bool IsListening => _running;
+
     /// <summary>True while a client is connected.</summary>
     public bool IsClientConnected => _clientConnected;