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>

CMakeLists.txt

@@ -253,6 +253,7 @@ if(BT_GLASS)
     "engine/MUNGA_L4/L4PADRIO.cpp"
     "engine/MUNGA_L4/L4PADBINDINGS.cpp"
     "engine/MUNGA_L4/L4PADPANEL.cpp"
+    "engine/MUNGA_L4/L4GLASSWIN.cpp"
     "engine/MUNGA_L4/L4PLASMAWIN.cpp"
   )
 endif()