fix: L37 Core compile error (stray paren) and Unreal-side issues from review R2

ShapeWorldInternal.h kept an extra ')' after a diagnostic edit was restored post-build, so the L37
commit did not compile; the fixed build reproduces L37's verified owner-world hashes exactly.
Unreal (uncompiled here): SetHardTransitionFallbackForAssembly is const over a mutable runtime flag
(the adapter calls it through a const manager); the legacy fallback clears the flag; VoxelStrateManager
includes <cmath> for std::llround. Adds research R2 (read-only Unreal compile/behaviour review).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Source/VoxelForge/Private/VoxelStrateManager.cpp

@@ -13,6 +13,7 @@
 #include "VoxelTerrainOpDefinition.h"  // For UVoxelTerrainOpDefinition::ApplyTo
 #include "VoxelBiomeDefinition.h"  // For UVoxelBiomeDefinition (biome context flatten)
 #include "HAL/IConsoleManager.h"
+#include <cmath>  // std::llround
 #include "Misc/CommandLine.h"
 #include "Misc/Crc.h"
 #include "Misc/Parse.h"

Source/VoxelForge/Private/VoxelWorld.cpp

@@ -7771,6 +7771,12 @@ void AVoxelWorld::FallBackToLegacyAfterCoreInitializationFailure(const FString&
     VoxelForgeCoreWorldAssemblyJson.Reset();
     VoxelForgeCoreWorldAssemblyHash.Reset();
     bUseVoxelForgeCore = false;
+    // The Core adapter sets this before validation; legacy generation must not inherit it.
+    // L'adaptateur Core l'active avant validation ; le générateur historique ne doit pas en hériter.
+    if (StrateManager != nullptr)
+    {
+        StrateManager->SetHardTransitionFallbackForAssembly(false);
+    }
     CoreFallbackCenterLocalCm = FVector::ZeroVector;
     if (Mesher != nullptr)
     {