vehicleSubSystems: verify Phase 1 end-to-end + confirm the Phase-2 blocker

Add a BT_VSS_LOG diagnostic (Make entry + per-subsystem classID/auxScreen dump +
the ConfigureForModel path).  Verified under BT_DEV_GAUGES: the gauge renderer
builds, ConfigureForModel(Init) runs bhk1Init, and VehicleSubSystems::Make is
called with the full 33-subsystem roster -- the dispatcher iterates every
subsystem and its classID switch resolves the displayable types (0xBC3 Sensor,
0xBC6 Myomers, 0xBC8/0xBD4 Emitter/PPC, 0xBCD/0xBD0 Proj/Missile).

CONFIRMED (empirically) the Phase-2 blocker: subsystem[0x1dc] (the aux-screen
position the Make gates on) reads 0xCDCDCDCD (uninitialized) / garbage for the
displayable subsystems -> every panel hits the "Illegal aux screen position"
skip, so nothing renders yet.  Phase 2 = populate the aux-screen field from the
subsystem resource.  Combat remains un-regressed (the skip path is inert).

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

game/reconstructed/btl4app.cpp

@@ -645,6 +645,9 @@ BTL4Application::SharedData
 		BTL4GaugeRenderer
 			*gauge_renderer = (BTL4GaugeRenderer*)GetGaugeRenderer();	// *(this+0x4c)
 
+		if (getenv("BT_VSS_LOG"))
+			DEBUG_STREAM << "[vss] MakeViewpointEntity: gaugeRenderer="
+						<< (int)(gauge_renderer != NULL) << " -> ConfigureForModel(Init)\n" << std::flush;
 		if (gauge_renderer != NULL)
 		{
 			gauge_renderer->ConfigureForModel("Init", viewing_entity);	// FUN_0046ff64

game/reconstructed/btl4gau2.cpp

@@ -1371,6 +1371,8 @@ Logical
 		imageNames[p] = methodDescription.parameterList[p].data.string;
 
 	int count = entity->GetSubsystemCount();				// entity+0x124
+	if (getenv("BT_VSS_LOG"))
+		DEBUG_STREAM << "[vss] Make called: subsystemCount=" << count << "\n" << std::flush;
 	for (int i = 0; i < count; i++)
 	{
 		if (i == 0)											// slot 0 = the controls mapper
@@ -1382,6 +1384,9 @@ Logical
 			continue;
 
 		int group = *(int *)((char *)sub + 0x1dc) - 1;		// aux-screen position 1..12
+		if (getenv("BT_VSS_LOG"))
+			DEBUG_STREAM << "[vss] i=" << i << " classID=" << (int)sub->GetClassID()
+						<< " auxScreen[0x1dc]=" << (group + 1) << "\n" << std::flush;
 		if (group < 0)
 		{
 			DebugStream << "Auxiliary screen position = zero\n";