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

Wires LogPushBackDispatch into the modern FindCollisions overload
at the entry block (after path/collisions/obj locals + movement
computed). Legacy overload at line ~1895 delegates to modern, so
single instrumentation site covers all dispatches.

returnState=-1 sentinel marks "entry log" — A6.P2 analysis pairs
each entry with subsequent [push-back] adjust-sphere lines and
the eventual return state.

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

src/AcDream.Core/Physics/BSPQuery.cs

@@ -1611,6 +1611,23 @@ public static class BSPQuery
 
         var movement = sphere0.Center - localCurrCenter;
 
+        // A6.P1: snapshot dispatcher entry for the [push-back-disp] probe.
+        // Emitted before path selection so the captured state reflects
+        // the inputs the dispatcher routes on. The returnState=-1 sentinel
+        // marks "entry log" — A6.P2 analysis pairs entry with the
+        // subsequent [push-back] adjust-sphere lines and inferred return.
+        if (PhysicsDiagnostics.ProbePushBackEnabled)
+        {
+            PhysicsDiagnostics.LogPushBackDispatch(
+                sphereCenter:    sphere0.Center,
+                movement:        movement,
+                collide:         path.Collide,
+                insertType:      (int)path.InsertType,
+                objState:        unchecked((int)obj.State),
+                walkInterpEntry: path.WalkInterp,
+                returnState:     -1);
+        }
+
         // Helper: transform a local-space vector to world space.
         // ACE: path.LocalSpacePos.LocalToGlobalVec(v)
         Vector3 L2W(Vector3 v) => Vector3.Transform(v, localToWorld);