refactor(sheets, settings): drop the last sheet-ring remnants and dead settings

The far sheet ring was already gone from the runtime; this removes what
was left of it:
- UVoxelSettings::bFarSheetRing / FarSheetSpanLevels, the
  voxel.TestFarSheetRing switch, and their log/trace/dump fields.
- The sheet branch of VoxelClipmapDesiredTiles (FParameters sheet fields,
  OuterShell sheet level, sheet ring emission). Output for the runtime
  configuration (sheet off) is unchanged: same rings, same alignment.
- Tests: VerticalStrateReach now asserts the sheet-free selector (its
  expected counts were stale since the aligned-ring change 85a803b:
  LOD0 343 -> 512); ClipmapNoOverlap drops the sheet sweep cases and the
  frozen 7486c29 oracle's sheet branch. New expected values were computed
  with a Python port of the selector that reproduces the test's existing
  635/594487 and 508/74295 measurements exactly; all 5,145 sweep cases
  pass (no overlap, full coverage).
- Tools/VoxelForgeTest.ps1 no longer passes voxel.TestFarSheetRing or
  reports far_sheet_ring. The sheet_tile dump field is kept (the parity
  compare reads it).

Also removes settings nothing reads: CeilingViewMultiplier,
CeilingBandChunks (pre-clipmap ceiling band) and DensityVolumeMaxTasks
(the volume fill runs on its own thread). Saved assets that still carry
these values load normally; the values are ignored.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01URDGLsu7c4nunqNFPJEFPU

Tools/VoxelForgeTest.ps1

@@ -54,7 +54,6 @@ $HorizonMetrics = [ordered]@{
     status = 'not_run'
     level = $HorizonLevel
     render_distance_chunks = $HorizonRenderDistanceChunks
-    far_sheet_ring = $false
 }
 $HorizonRenderMetrics = [ordered]@{ requested = $Scenario -eq 'horizon-render'; status = 'not_run' }
 $DeterminismEvidence = [ordered]@{ requested = $Scenario -eq 'determinism'; status = 'not_run' }
@@ -1293,7 +1292,6 @@ try {
             $tracePath = Join-Path $RunRoot 'horizon_trace.jsonl'
             $baseCvars['voxel.TestRenderDistanceChunks'] = $HorizonRenderDistanceChunks
             $baseCvars['voxel.TestMaxClipLevel'] = $HorizonLevel
-            $baseCvars['voxel.TestFarSheetRing'] = 0
             $baseCvars['voxel.StartupTraceFile'] = $tracePath
             $baseCvars['voxel.StartupTraceMaxTiles'] = 16384
             $baseCvars['voxel.TestExitOnSteady'] = 1
@@ -1311,7 +1309,6 @@ try {
             $tracePath = Join-Path $RunRoot 'horizon_render_trace.jsonl'
             $baseCvars['voxel.TestRenderDistanceChunks'] = $HorizonRenderDistanceChunks
             $baseCvars['voxel.TestMaxClipLevel'] = $HorizonLevel
-            $baseCvars['voxel.TestFarSheetRing'] = 0
             $baseCvars['voxel.StartupTraceFile'] = $tracePath
             $baseCvars['voxel.StartupTraceMaxTiles'] = 16384
             $baseCvars['voxel.TestCeilingView'] = 1
@@ -1340,7 +1337,6 @@ try {
             $determinismBase = [ordered]@{
                 'voxel.TestRenderDistanceChunks' = $HorizonRenderDistanceChunks
                 'voxel.TestMaxClipLevel' = $HorizonLevel
-                'voxel.TestFarSheetRing' = 0
                 'voxel.TestExitOnSteady' = 1
                 'voxel.StartupTraceMaxTiles' = 16384
                 'voxel.OuterClassifierMode' = 0
@@ -1369,7 +1365,6 @@ try {
             $DeterminismEvidence = Compare-DeterminismDumps $defaultDump $crtFma3OffDump
             $DeterminismEvidence.level = $HorizonLevel
             $DeterminismEvidence.render_distance_chunks = $HorizonRenderDistanceChunks
-            $DeterminismEvidence.far_sheet_ring = $false
             $DeterminismEvidence.default_measurement = $defaultMetrics
             $DeterminismEvidence.crt_fma3_off_measurement = $crtFma3OffMetrics
             $GameMetrics = $crtFma3OffMetrics