wip(assembler): round S9 -- collision look-ahead: ground ring ready on arrival up to 40 m/s and 50 m/s falls

voxel.StreamingCollisionLookahead (default on) predicts the support tile 350 ms
ahead along full 3D velocity and prioritises its 9-tile collision ring. Owner
plan, BuildHost actor: 40 m/s arrival-ready 25/74 -> 74/74 (CVar-off control
15/74); 6/12/25 m/s stay 100%; -Z 50 m/s 93/93. Spawn unchanged (~7.7 s).
Critical LOD0 path at 40 m/s: generation 67 ms p50, RMC body update 38 ms p50.
LOD8 cost counted (native horizon 48 ms of 60), optimisation deferred.

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

Source/VoxelForge/Public/VoxelWorld.h

@@ -702,6 +702,10 @@ private:
     void BuildCoreDesiredTiles(const FIntVector& Center, const FVector& PlayerPosition,
                                APawn* PlayerPawn, const FVector& PlayerHeading,
                                TArray<FVoxelTileKey>& OutLeavers);
+    FIntVector GetStreamingHeadingStep(const FVector& PlayerHeading,
+                                       const APawn* PlayerPawn) const;
+    int32 GetStreamingCollisionLookaheadTiles(const FVector& PlayerHeading,
+                                              const FIntVector& HeadingStep) const;
     void StartPendingCoreRegionCompile();
     void LoadCoreTile(const FVoxelTileKey& Tile, EVoxelTileWorkPriority WorkPriority);
     void EnqueueStreamingResult(FChunkResult&& Result);