diag(phys): A6.P5 [cellset-build] probe — log BuildCellSetAndPickContaining output

One [cellset-build] line per call when ACDREAM_PROBE_CELLSET=1: seed cell,
sphere world XY, candidate count, full candidate id list. Used to prove
the cellSet for the player's start cell doesn't include the door's outdoor
cell across the over-penetration tick.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/CellTransit.cs

@@ -494,6 +494,11 @@ public static class CellTransit
             }
         }
 
+        if (PhysicsDiagnostics.ProbeCellSetEnabled)
+        {
+            PhysicsDiagnostics.LogCellSetBuild(currentCellId, worldSphereCenter, candidates);
+        }
+
         // Containment test: for each candidate, transform worldSphereCenter to
         // local and test PointInsideCellBsp.
         foreach (uint candId in candidates)