Workstream A prototype: play without the cockpit

Splits the control surface the game consumes from the RIO board into
RIOBase (8 virtuals + the five analog scalars); the serial RIO is now one
implementation of it. Adds two new ones:

- PadRIO (L4CONTROLS=PAD): in-process RIO speaking the full surface from
  an XInput controller + PC keyboard using vRIO's default profile (left
  stick/WASD = stick, triggers/Q,E = pedals, right stick Y/PgUp,PgDn =
  rate throttle that holds position, A/Space = trigger, B/R = reverse,
  dpad/arrows = hat, Start,Back/F1,F2 = config). Samples in GetNextEvent
  so button latency does not depend on the 15 s menu-time analog cadence;
  hot-plugs pads; L4PADFLIP=XY inverts stick axes; lamp commands land in
  lampState[] for the planned on-screen cockpit panel. The stock
  VTVRIOMapper/lamp/button path runs unchanged.

- PlasmaScreen (L4PLASMA=SCREEN): the 128x32 plasma glass as a desktop
  window in plasma orange (L4PLASMASCALE, default x4), rendering the same
  Video8BitBuffered surface the gauge system always drew; no COM port.

Verified in the sandbox with vRIO off and no serial devices: boots to a
running mission, controller hot-detected, plasma window drawing live game
content (score readout). BUILD.md 4 documents the desktop environ.ini and
bindings; roadmap updated.

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

MUNGA_L4/L4CTRL.cpp

@@ -1,6 +1,8 @@
 #include "mungal4.h"
 #pragma hdrstop
 
+#include "l4padrio.h"
+
 #include "l4ctrl.h"
 #include "l4keybd.h"
 #include "l4app.h"
@@ -830,6 +832,19 @@ LBE4ControlsManager::LBE4ControlsManager():
 					joystickPointer = NULL;
 				}
 			}
+			else if (strcmpi(temp, "PAD") == 0)
+			{
+				//------------------------------------------------------
+				// Cockpit-less play: PadRIO speaks the RIO control
+				// surface from an XInput pad + the PC keyboard, so the
+				// full RIO mapper/lamp/button path runs unchanged.
+				//------------------------------------------------------
+				rioPointer = new PadRIO();
+				Check(rioPointer);
+				Register_Object(rioPointer);
+				flags.RIOExists = 1;
+				primaryControlType = LBE4ControlsManager::PrimaryRIO;
+			}
 		}
 		while (temp[0] != '\0');
 	}