feat(battle-engine): BestHTTP SocketIO + Spine SDK member shims (1556->1462)

BestHTTP.SocketIO: Socket.On/Off/Emit + SocketIOCallback delegate, SocketManager ctors/
State/Socket/indexer/Open/Close/SettingRealtimeNetworkAgent, SocketOptions. Spine: Skeleton
(Data/Skin/Scale/FindBone/SetSkin/Update), Bone (WorldX/Y/RotationX), SkeletonMecanim
(MonoBehaviour + skeleton). All minimal hand shims (no full-surface -> no SDK closure pull);
node-socket path is Phase-2, off the battle path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

SVSim.BattleEngine/Shim/External/SdkStubs.cs

@@ -38,8 +38,38 @@ namespace CodeStage.AntiCheat.ObscuredTypes
 }
 
 // ---- Spine animation ----
-namespace Spine { public class Bone { } internal class _ShimAnchor { } }
-namespace Spine.Unity { public class SkeletonMecanim { } internal class _ShimAnchor { } }
+namespace Spine
+{
+    // Spine runtime — minimal hand shim (cosmetic skeletal animation, off battle path).
+    public class SkeletonData { }
+    public class Skin { }
+    public class Bone
+    {
+        public float WorldX, WorldY, WorldRotationX;
+        public Skeleton Skeleton => null;
+    }
+    public class Skeleton
+    {
+        public SkeletonData Data => null;
+        public Skin Skin => null;
+        public float ScaleX, ScaleY;
+        public Bone FindBone(string boneName) => null;
+        public void SetSkin(string skinName) { }
+        public void SetSkin(Skin newSkin) { }
+        public void SetSlotsToSetupPose() { }
+        public void Update(float delta) { }
+    }
+    internal class _ShimAnchor { }
+}
+namespace Spine.Unity
+{
+    public class SkeletonMecanim : UnityEngine.MonoBehaviour
+    {
+        public Spine.Skeleton skeleton => null;
+        public Spine.Skeleton Skeleton => null;
+    }
+    internal class _ShimAnchor { }
+}
 
 // ---- misc third-party namespaces (anchors) ----
 namespace RedShellUnity { internal class _ShimAnchor { } }