feat(phys): ShadowEntry adds LocalPosition + LocalRotation

Local-to-entity transform fields, default-valued so existing single-shape
callers keep working unchanged. RegisterMultiPart (next commit) populates
them per part so UpdatePosition can rebuild the entry's world Position +
Rotation when the entity moves.

All 24 existing ShadowObjectRegistry tests pass (including the 2 new
slice 1 tests from b49ed90).

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

src/AcDream.Core/Physics/ShadowObjectRegistry.cs

@@ -431,4 +431,11 @@ public readonly record struct ShadowEntry(
     /// from <c>PWD._bitfield</c> at <c>CreateObject</c> time via
     /// <see cref="EntityCollisionFlagsExt.FromPwdBitfield(uint)"/>.
     /// </summary>
-    EntityCollisionFlags Flags = EntityCollisionFlags.None);
+    EntityCollisionFlags Flags = EntityCollisionFlags.None,
+    // A6.P4 door fix (2026-05-24): local-to-entity transform for multi-part
+    // entities. ShadowObjectRegistry.UpdatePosition uses these to rebuild
+    // Position/Rotation when the entity moves. Single-shape callers leave
+    // these at default (zero offset, identity rotation) — equivalent to
+    // the shape sitting at the entity's origin.
+    Vector3 LocalPosition = default,
+    Quaternion LocalRotation = default);