feat(physics): A6.P1 — instrument CheckOtherCells with [push-back-cell]

Wires LogPushBackCellTransit into the multi-cell BSP iteration loop
just before ApplyOtherCellResult halts. Captures primary/other
cell ids + BSP result for direct comparison to retail's
CTransition::check_other_cells loop (already ported as A4).

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

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -1469,6 +1469,15 @@ public sealed class Transition
                     $"[other-cells] primary=0x{sp.CheckCellId:X8} iter=0x{cellId:X8} result={result}"));
             }
 
+            if (PhysicsDiagnostics.ProbePushBackEnabled)
+            {
+                PhysicsDiagnostics.LogPushBackCellTransit(
+                    primaryCellId: sp.CheckCellId,
+                    otherCellId:   cellId,
+                    bspResult:     (int)result,
+                    halted:        false);
+            }
+
             if (ApplyOtherCellResult(result, out var halted))
                 return halted;
         }