perf(core): FI LOD0 attribution, exact Z-inner traversal; fix a mesh gap at the passage shaft foot (L57); R26

Sampled cycle attribution of FI LOD0 field work: grid fill 83%, boundary 13%, skirts 4%; island roots,
columns and helix dominate, the column cache path is real but secondary (no thrashing). FI-only Z-inner
traversal at LOD0 (same lattice samples, exact) cuts FI whole view 5.35 -> 5.03 s and moving p50 by 12%;
global Z-inner and <=4-island culling were measured and rejected. The meshing band now includes the planned
passage support column's conservative bounds, closing a real gap where the arrival shaft meets the floor
(WorldAssemblyEvaluatorVersion 208 -> 209). fast/medium/full PASS, Clang and GCC.
Research R26 (self-checked): native lattice (maze/shaft) generator design.

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

Standalone/Core/src/CoreNamespacePreamble.h

@@ -56,6 +56,7 @@
 #include "VoxelForgeCore/VoxelForgeCore.h"
 #include "VoxelForgeCore/ThreadLocalStorage.h"
 #include "VoxelForgeCore/SharedColumnCache.h"
+#include "VoxelForgeCore/FloatingIslandInstrumentation.h"
 
 // Keep Core's expression-level FMA behavior fixed regardless of the toolchain setting.
 // Clang's "fast" mode ignores the pragma, so Core's runtime self-test rejects that build.