vehicleSubSystems Phase 1: reconstruct + register the cluster-panel family

Reconstruct the whole engineering-screen (MFD) subsystem cluster-panel system in
btl4gau2 (from the Ghidra decomp of BTL4OPT.EXE) and register the vehicleSubSystems
config primitive:

- Sub-gauges: AnimatedSubsystemLamp/AnimatedSourceLamp (OneOfSeveral + cooling/
  power connections), ScalarBarGauge (BarGraphBitMapScalar + generator-voltage
  connection), ConfigMapGauge, plus the 3 file-private GaugeConnection classes
  (@004c3134/31ec/3288 samplers).
- SubsystemCluster base (ctor builds ~11 child gauges across the MFD + engineering
  ports; Execute/dtor/frame-draw/enable helpers) + the 5 subclasses HeatSink/
  Myomer/Weapon/Energy/Ballistic (ctors + Executes).
- VehicleSubSystems::Make dispatcher (@004cbaf0): per-subsystem factory keyed on
  classID (HeatSink 0xBC3 / Myomer 0xBC6 / Energy 0xBC8,0xBD4 / Ballistic
  0xBCD,0xBD0), placed via the 12-row aux-screen geometry table, + registered in
  BTL4MethodDescription[].

SAFE + gated: gauges only build under BT_DEV_GAUGES/pod, and until Phase 2
populates the subsystem aux-screen field (subsystem[0x1dc]) the Make hits its
"aux screen = zero" skip -> combat untouched.  Two minor children deferred as
marked NULLs (SegmentArc270 recharge dial + BitMapInverseWipeScalar eject wipe --
their ctors are btl4gaug placeholders).  Raw-offset subsystem reads (0x1dc/0x1e0/
0x1e4/0x31c/0x334/0x364/0x43c...) marked BEST-EFFORT pending Phase 2.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

game/reconstructed/btl4grnd.cpp

@@ -66,6 +66,7 @@
 #endif
 #if !defined(BTL4GAUG_HPP)
 #	include <btl4gaug.hpp>		// the BT gauge classes (Compass, etc.)
+#	include <btl4gau2.hpp>		// the composite cluster gauges + VehicleSubSystems
 #	include <btl4rdr.hpp>		// MapDisplay (the "map" radar gauge)
 #	include <btl4gau3.hpp>		// PlayerStatus (the comm/score gauge)
 #endif
@@ -141,6 +142,7 @@ MethodDescription
 			&OneOfSeveralPixInt::methodDescription,		// "oneOfSeveralPixInt" -- button-state lamp (duck/light/mode)
 			&MapDisplay::methodDescription,				// "map" -- the radar / tactical display
 			&PlayerStatus::methodDescription,			// "PlayerStatus" -- comm/score name-tag gauge
+			&VehicleSubSystems::methodDescription,		// "vehicleSubSystems" -- engineering-screen subsystem cluster panels
 			&BTL4ChainToPrevious
 		};