fix(physics): push-out when spawned inside objects (stuck prevention)

When collision is detected at t=0 (already overlapping at step start),
push the sphere out along the collision normal by half-radius instead
of trying to slide with zero displacement (which gets stuck).

Returns Adjusted instead of Slid so the transition loop retries
from the pushed-out position.

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

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -752,11 +752,23 @@ public sealed class Transition
         if (bestT >= float.MaxValue)
             return TransitionState.OK; // no collision
 
+        // Already overlapping at the START of the step (bestT == 0 or very small).
+        // This happens when the player spawns inside an object or a previous
+        // step left them penetrating. Push out along the collision normal
+        // instead of sliding — sliding with zero displacement gets stuck.
+        if (bestT <= PhysicsGlobals.EPSILON)
+        {
+            Vector3 pushOut = bestNormal * (sphereRadius * 0.5f + 0.01f);
+            sp.AddOffsetToCheckPos(pushOut);
+            ci.SetCollisionNormal(bestNormal);
+            ci.SetSlidingNormal(bestNormal);
+            return TransitionState.Adjusted;
+        }
+
         // Rewind the sphere to the contact point (before penetration).
         if (bestT < 1f)
         {
             Vector3 contactPos = currPos + movement * bestT;
-            // Push slightly back along normal to prevent sitting exactly on the surface.
             contactPos += bestNormal * 0.005f;
             sp.SetCheckPos(contactPos, sp.CheckCellId);
         }