fix(physics): increase contact point safety margin

Rewind to t-0.02 instead of exact contact time, plus 2cm normal
push-back. The previous 0.5cm was too small — at high speed the
sub-step could overshoot past the surface.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -774,11 +774,14 @@ public sealed class Transition
             return TransitionState.Adjusted;
         }
 
-        // Rewind the sphere to the contact point (before penetration).
+        // Rewind the sphere to just BEFORE the contact point.
+        // Use t slightly before bestT to ensure no penetration.
         if (bestT < 1f)
         {
-            Vector3 contactPos = currPos + movement * bestT;
-            contactPos += bestNormal * 0.005f;
+            float safeT = MathF.Max(0f, bestT - 0.02f);
+            Vector3 contactPos = currPos + movement * safeT;
+            // Additional push along normal to clear the surface.
+            contactPos += bestNormal * 0.02f;
             sp.SetCheckPos(contactPos, sp.CheckCellId);
         }