standalone: shape-world look round 2 -- shards gone, calmer layered relief, still 0.72 s / 1.6 s cold

- Removed the thin automatic room-support slabs that left floating caps (in-view detached thin
  sheets 9 -> 0; the audit now also fails on isolated small components).
- Bounded 16-voxel floor/wall blend (18 rejected: it created a sub-voxel sheet), 3-voxel
  strata/cave blend, C1 tunnel radius profile (0 radius/slope steps at joins).
- Surface relief: broad octave with amplitude modulation instead of uniform bumps.
- Cold, no cache: 64 m full detail 0.924 s (8 workers) / 0.715 s (16); whole view 2.016 / 1.605 s.
- 1-worker and 6-worker hashes match; 5,642/5,642 passage samples open.
Not solved: regular bands in the narrow passage shafts, a few slivers on tile boundaries, faint
wall/floor plates; close-view mean surface distance to the owner field got worse (see REPORT.md).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Source/StreamingWorld.h

@@ -285,7 +285,7 @@ public:
                                            bool bInHashDensity=false,
                                            const FStandaloneMeshCache* InMeshCache=nullptr,
                                            int32 InMaxLevelFilter=-1)
-        :World(&InWorld),WorkerCount(FMath::Clamp(InWorkerCount,1,8)),bHashDensity(bInHashDensity),
+        :World(&InWorld),WorkerCount(FMath::Clamp(InWorkerCount,1,16)),bHashDensity(bInHashDensity),
          MeshCache(InMeshCache),MaxLevelFilter(InMaxLevelFilter)
     {
         VoxelGenLOD::InitializeConsoleSwitches();