feat(battle-engine): full Unity/VFX/god-object shims + expanded copy closure (2570 files)

Authored Unity primitive/object-model shim, VFX layer (control-flow-preserving, InstantVfx never invokes its action -- headless suppression), god-object stubs (GameMgr/EffectMgr/UIManager with faithfully-extracted nested enums), View/UI/Touch tree, LitJson+BetterList+Tuple copied, third-party stubs. Discovered Roslyn header-error masking: fixing class-header type errors unmasks body references, so the true copy closure is ~2570 files (was 782 under masking). Errors: masked-25720 -> 268; our shim files compile clean. Remaining: ~50 residual shim/external types, 24 NGUI UI-base overrides, static-type fixes, plus likely 1-2 more unmask waves.

SVSim.BattleEngine/Shim/External/ThirdParty.cs

@@ -0,0 +1,44 @@
+// AUTHORED SHIM (not copied). Third-party / platform SDK surface referenced by
+// tangentially-pulled engine files (audio, Steam, networking, serialization).
+// Stubbed minimally in their original namespaces; none is on the battle-resolution
+// path. Members grow only if the compile loop demands them.
+using System;
+
+// ---- remaining UnityEngine types ----
+namespace UnityEngine
+{
+    public class Font : Object { }
+    public enum Space { World, Self }
+    // NGUI's UIInputOnGUI reads Event.current (legacy IMGUI event).
+    public class Event { public static Event current => null; }
+}
+
+namespace UnityEngine.Networking
+{
+    public class UnityWebRequest : IDisposable { public void Dispose() { } }
+}
+
+// ---- CRI Atom audio middleware ----
+namespace CriWare
+{
+    public class CriAtomSource { }
+    public class CriAtom { }
+}
+
+// ---- Steamworks.NET ----
+namespace Steamworks
+{
+    public struct GetAuthSessionTicketResponse_t { }
+}
+
+// ---- BestHTTP Socket.IO ----
+namespace BestHTTP.SocketIO
+{
+    public interface IManager { }
+}
+
+// ---- Google Play Games ----
+namespace GooglePlayGames.BasicApi.Events
+{
+    public class Event { }
+}