wip(assembler): round L9 -- LOD1 skips proven-uniform blocks: 95% fewer samples, view ~2% faster

Step-2 (LOD1) tiles of native SurfaceWorld now prove 8-cell blocks uniform from exact heightfield
column extrema over the padded block (cells + normal halo) and skip their density fill; features,
edits, mixed strata and Unknown verdicts still fill. LOD1 samples 42,875 -> 2,063 per tile.
Audit: 80,502 skipped blocks (3 seeds) + 9,216 island blocks force-filled, 0 violations. All
SurfaceWorld and FloatingIslands hashes unchanged at W1/W8/W12, Clang off and GCC default.
Reviewer interleaved W12, no hashing: whole view 1.439 -> 1.409 s. L8 phase probes removed;
--profile-lod-work and --audit-uniform-block-proofs are opt-in.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Source/StreamingWorld.h

@@ -650,6 +650,8 @@ public:
 
     void SetMesherStageProfilingEnabled(bool Enabled)
     {bProfileMesherStages=Enabled;}
+    void SetUniformBlockProofAuditEnabled(bool Enabled)
+    {bAuditUniformBlockProofs=Enabled;}
     FStandaloneCpuTile GenerateDiagnostic(const FVoxelTileKey& Key,
         std::uint32_t GlobalOctaveDrop=0,std::uint32_t CellStride=1,
         bool ForceGenerate=false)
@@ -821,6 +823,7 @@ private:
             Options.useSharedColumnCache=bSharedColumnCache;
             Options.lod8HorizonInteriorStepVoxels=Lod8HorizonInteriorStepVoxels;
             Options.profileMesherStages=bProfileMesherStages&&!ForceGenerate;
+            Options.auditUniformBlockProofs=bAuditUniformBlockProofs&&!ForceGenerate;
             Options.diagnosticGlobalOctaveDrop=DiagnosticGlobalOctaveDrop;
             Options.diagnosticCellStride=std::max<std::uint32_t>(1,DiagnosticCellStride);
             Options.diagnosticColumnInterpolationStride=
@@ -999,6 +1002,7 @@ private:
     bool bSharedColumnCache=true;
     int32 Lod8HorizonInteriorStepVoxels=0;
     bool bProfileMesherStages=false;
+    bool bAuditUniformBlockProofs=false;
     std::atomic<uint64> CacheHitCount{0};
     mutable std::mutex Mutex;
     std::condition_variable Wake;