Glass cockpit: per-display windows (BT_GLASS_PANELS)

Break the desktop glass cockpit's secondary displays out of the single
combined pad panel + D3D gauge strip into ONE window per pod display, each
carrying that display's surface with its RIO button bank, arranged
pod-faithfully around the main view.  New TU engine/MUNGA_L4/L4GLASSWIN.*
(BT_GLASS-only), selected by the -platform glass preset via the new runtime
gate BT_GLASS_PANELS (=0 falls back to the legacy single panel + dock).

- Surfaces are CPU-expanded from the shared gauge buffer
  (SVGA16::ExpandPlaneToBGRA, no D3D) and StretchDIBits'd in -- the D3D
  dev-composite path (dock / window / overlay) stands down while active.
- Buttons sit UNDER the imagery: big hidden click targets that reach into
  the display, with only a small protruding edge showing as a lamp light.
  Red MFD banks tile the top/bottom; radar rails run the sides + a bottom
  row; a Flight Controls window hosts the no-display banks.
- Windows: Heat / Engineering / Comm / Left Weapons / Right Weapons / radar
  + Flight Controls; edge-to-edge (no in-client margin/title; OS caption
  labels each).
- Fix blank surfaces: application/ghWnd are duplicate-defined and bind
  non-deterministically under /FORCE, so the fresh L4GLASSWIN TU read NULL.
  Reach the renderer/window via BTResolveGaugeRenderer/BTResolveMainWindow
  defined in btl4main.cpp off the real btl4App/hWnd pointers.  New gotcha:
  reconstruction-gotchas.md S6 duplicate-GLOBAL corollary.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

engine/MUNGA_L4/L4PADRIO.cpp

@@ -9,6 +9,7 @@
 
 #include "l4padrio.h"
 #include "l4padpanel.h"
+#include "l4glasswin.h"
 #include "l4ctrl.h"
 
 #include <windows.h>
@@ -168,10 +169,16 @@ PadRIO::PadRIO():
 		<< "live on focus; L4PADFLIP=" << flipStickAxes << ")\n" << std::flush;
 
 	//
-	// The on-screen cockpit button panel (step 2d) rides the device: the
-	// glass preset sets BT_PAD_PANEL=1.
+	// The on-screen cockpit buttons ride the device.  BT_GLASS_PANELS (the
+	// glass preset default) breaks each secondary display into its own window
+	// with its RIO bank around it; otherwise the single combined pad panel
+	// (BT_PAD_PANEL=1) is used.
 	//
-	if (getenv("BT_PAD_PANEL") != NULL && *getenv("BT_PAD_PANEL") != '0')
+	if (BTGlassPanelsActive())
+	{
+		BTGlassPanels_Create();
+	}
+	else if (getenv("BT_PAD_PANEL") != NULL && *getenv("BT_PAD_PANEL") != '0')
 	{
 		BTPadPanel_Create();
 	}
@@ -179,6 +186,7 @@ PadRIO::PadRIO():
 
 PadRIO::~PadRIO()
 {
+	BTGlassPanels_Destroy();	// safe no-op if the glass windows were never created
 	BTPadPanel_Destroy();
 	if (activeInstance == this)
 	{