[idd] input: receive LGMP input reports

Add an optional input transport and a dedicated LGMP receiver that
validates source ownership, generations, ordered sequences, and leases.

Poll input outside the 10 ms control timer. Forward mouse and keyboard
state through the LGInput pipe, and neutralize the endpoint before
ownership changes or transport failures can leave input held.

idd/LGIdd/transport/IInputTransport.h

@@ -0,0 +1,32 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#pragma once
+
+class IInputSink;
+
+class IInputTransport
+{
+public:
+  virtual ~IInputTransport() = default;
+
+  virtual bool Start(IInputSink& sink) = 0;
+  virtual void Stop() = 0;
+};