engine cleanup passes 4-7 + multi-instancing ambient rip

Squashes 146 commits from battle-engine-extraction. Net: 2,045 files changed,
+11,896 / -158,687 lines. Ships engine passes 4-7 (dead-code cull, view-layer
stub, receive-path shrink) plus the Phase-5 AsyncLocal ambient deletion that
turns concurrent battles into a type-system property rather than a scope
contract.

## What landed

**Passes 4-7 (chunks 1-34):** Extended the Phase-4 const-false collapse into a
cascading cull across the skill graph, view layer, and receive-path periphery.
Six mode flags (IsWatchBattle/IsReplayBattle/IsAdmin/IsAdminWatch/IsPuzzleQuest/
IsAINetwork) became `const false`, every guarded block deleted. Field*.cs
subclass ctors + BackGroundBase + ObjectChecker culled to no-ops. Mulligan
family reworked to take a mgr param through IMulliganMgr.InitMulligan.
Emotion/Recovery/Resource clusters null-stubbed. Prediction/OperationSimulator/
skill filters converted from static ambient reads to per-mgr reads via
SkillPrm.ownerCard.SelfBattlePlayer.BattleMgr / ins.BattleMgr / this.BattleMgr.

**Phase-5 ambient rip (chunks 35-47):** Deleted BattleAmbient / BattleAmbient-
Context / TestBattleScope in full. Every per-battle mutable slot now lives on
the mgr instance itself:
  mgr.InstanceIsForecast / InstanceIsRandomDraw / InstanceRecoveryInfo /
  InstanceViewerId / InstanceNetworkAgent / GameMgr
BattleManagerBase.GetIns() returns null unconditionally; the residual static
flags + 3 façades (Certification.ViewerId, Data.BattleRecoveryInfo,
ToolboxGame.RealTimeNetworkAgent) are null-tolerant defaults kept for the
handful of engine-internal readers that still reference their types. Zero
BattleAmbient references anywhere in engine + node + tests.

Added pre-seeded GameMgr ctor overload threaded through the mgr chain
(BattleManagerBase → SingleBattleMgr / NetworkBattleManagerBase → NetworkStandard-
BattleMgr → HeadlessBattleMgr / HeadlessNetworkBattleMgr). Fixtures build a
GameMgr, seed it via HeadlessEngineEnv.SeedCharaIds/SeedNetUser, and pass it
to the mgr's ctor — no ambient reach.

Node side (SVSim.BattleNode/SessionBattleEngine): _ctx replaced with a plain
GameMgr field; 34 `using var _ambient = BattleAmbient.Enter(_ctx)` scope wraps
ripped from every accessor and mutator; EngineGlobalInit.WirePerSessionGameMgr
takes GameMgr as a param and runs from SessionBattleEngine.SetupInternal
BEFORE mgr construction.

Test side: TestBattleScope deleted; 18 fixture [SetUp]s migrated to
`HeadlessEngineEnv.EnsureProcessGlobals()`; MultiInstanceEngineTests rewritten
around per-mgr construction (GetIns() → null is the pinned invariant).

## Regression fixes

- **chunk-48** (MulliganCtrl): chunk-35's `= null` stubs on card lookups broke
  the live receive-driven Deal path (BattlePlayerBase.DrawCard NRE'd downstream
  of NetworkPlayerMulliganCtrl.StartMulliganVfx). Restored the three lookups
  via `_battlePlayer.BattleMgr.GetBattleCardIdx`. Engine tests were satisfied
  by the WireMulliganPhase seam; unit tests exposed the live-path gap.

## Ship state

- SVSim.BattleEngine.Tests: 56/56 pass, 2 skip
- SVSim.UnitTests: 1554/1554 pass (was 1523/31-fail before chunk 48)
- Solution build: 0 source warnings (40 pre-existing NU1902 MessagePack CVEs
  in SVSim.EmulatedEntrypoint, unrelated)
- Sequential PVP smoke: verified live (two back-to-back battles, no regression
  on cleanup/spinup)
- Concurrent PVP smoke: verified live

Adds tools/engine-port/ClosureAnalyzer/ — the Roslyn transitive-type-closure
analyzer needed to make future cascade cleanup safe (per feedback memory
"Engine cleanup needs closure tool" from the 2026-06-28 pass-3 failure).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleEngine/Shim/UnityEngine/UnityShim2.cs

@@ -8,8 +8,6 @@ namespace UnityEngine
 {
     public class TextAsset : Object
     {
-        public string text => "";
-        public byte[] bytes => new byte[0];
     }
 
     public class AsyncOperation
@@ -17,7 +15,6 @@ namespace UnityEngine
         public bool isDone => true;
         public float progress => 1f;
         public int priority { get; set; }
-        public bool allowSceneActivation { get; set; }
     }
 
     public class AssetBundle : Object
@@ -25,27 +22,22 @@ namespace UnityEngine
         public static AssetBundle LoadFromFile(string path) => null;
         public static AssetBundleCreateRequest LoadFromFileAsync(string path) => null;
         public string[] GetAllAssetNames() => new string[0];
-        public T LoadAsset<T>(string name) where T : Object => null;
-        public Object LoadAsset(string name) => null;
-        public Object[] LoadAllAssets() => new Object[0];
         public AssetBundleRequest LoadAllAssetsAsync() => null;
         public void Unload(bool unloadAllLoadedObjects) { }
     }
 
     public class AssetBundleCreateRequest : AsyncOperation { public AssetBundle assetBundle => null; }
-    public class AssetBundleRequest : AsyncOperation { public Object asset => null; public Object[] allAssets => new Object[0]; }
+    public class AssetBundleRequest : AsyncOperation { public Object[] allAssets => new Object[0]; }
 
     public class Collider2D : Component { public bool enabled { get; set; } }
-    public partial class BoxCollider2D : Collider2D { public bool isTrigger { get; set; } public Vector2 offset { get; set; } public Vector2 size { get; set; } }
+    public partial class BoxCollider2D : Collider2D { public Vector2 offset { get; set; } public Vector2 size { get; set; } }
     public partial class Light : Behaviour { }
     public class AudioListener : Behaviour { }
 
-    public enum RenderTextureFormat { ARGB32, Depth, ARGBHalf, ARGB64, Default }
+    public enum RenderTextureFormat { ARGB32, Default }
 
     public enum RuntimeInitializeLoadType
     {
-        AfterSceneLoad, BeforeSceneLoad, AfterAssembliesLoaded,
-        BeforeSplashScreen, SubsystemRegistration
     }
 
     public sealed class RuntimeInitializeOnLoadMethodAttribute : Attribute
@@ -56,19 +48,13 @@ namespace UnityEngine
 }
 
 // Sub-namespace anchors (referenced via `using`; types unmask in later waves if used).
-namespace UnityEngine.Experimental { internal class _ShimAnchor { } }
-namespace UnityEngine.Experimental.Rendering { internal class _ShimAnchor { } }
+namespace UnityEngine.Experimental { }
+namespace UnityEngine.Experimental.Rendering { }
 namespace UnityEngine.SceneManagement
 {
-    internal class _ShimAnchor { }
-    public struct Scene { public string name => ""; public int buildIndex => 0; public bool IsValid() => false; public bool isLoaded => false; }
     public static class SceneManager
     {
         public static void LoadScene(string sceneName) { }
-        public static void LoadScene(int sceneBuildIndex) { }
-        public static Scene GetActiveScene() => default;
-        public static Scene GetSceneByName(string name) => default;
-        public static int sceneCount => 0;
     }
 }
 namespace UnityEngine.SocialPlatforms
@@ -77,5 +63,4 @@ namespace UnityEngine.SocialPlatforms
     // Cute.IAchievementCallback; adding one here makes the unqualified name ambiguous.
     public interface IAchievement { }
     public interface IAchievementDescription { }
-    public interface ILocalUser { void Authenticate(System.Action<bool> callback); }
 }