feat(battle-engine-port): M2 step 1 — SingleBattleMgr constructs headless

First green of the M2 go/no-go probe: `new SingleBattleMgr(StandardBattleMgr-
ContentsCreator)` now builds the two-player pair fully headless against the shim,
no Unity runtime. Verdict: headless construction is feasible; every blocker was a
mechanical no-op shim fill or data seam, not a Unity/logic wall.

Shim fills (authored):
- GameMgr: lazy non-null DataMgr/PrefabMgr/InputMgr/SoundMgr/BattleControl.
- GameObject: lazy cached component model so GetComponent<T>/AddComponent<T> return
  non-null no-op instances for Component-derived T (F1: unguarded view touches).
- Resources.Load(string): cached non-null GameObject so the prefab->Instantiate->
  GetComponent chain (UnityEventAgent) yields a real object.
- ClassBattleCardViewBase: re-attach dropped IClassBattleCardView (no-op members);
  ClassBattleCardBase.Setup casts the created view to it.

Engine copy (DP1/DP3 mis-cut fix):
- CardIconControl.cs copied verbatim (manifested) + generated null-stub deleted.
  SplitAndCompleteIconStr is pure string logic on the resolution path that M1 had
  wrongly stubbed as "View" -> null deref in SkillCreator.CreateBuildInfo.

Test harness (SVSim.BattleEngine.Tests, authored fixture):
- HeadlessContentsCreator/HeadlessPhaseCreator: deterministic replica of the solo
  practice init (StandardBattleMgrContentsCreator + SingleBattlePhaseCreator) with
  no-op recovery/replay managers.
- HeadlessCardMaster: reflects the loader cards.json dump into CardMaster.
- HeadlessMasterData: minimal Data.Master (class-character list, empty collections)
  + Data.Load + player/enemy chara ids.
- ConstructionProbeTests.SingleBattleMgr_constructs_headless — GREEN.

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

SVSim.BattleEngine/Shim/GodObjects/GodObjects.cs

@@ -110,12 +110,15 @@ public class GameMgr
     private NetworkUserInfoData _netUser;
 
     public EffectMgr GetEffectMgr() => _effect ??= new EffectMgr();
-    public SoundMgr GetSoundMgr() => _sound;
-    public DataMgr GetDataMgr() => _data;
+    public SoundMgr GetSoundMgr() => _sound ??= new SoundMgr();
+    // Headless: hand back non-null no-op instances. The copied manager types are pure
+    // data/dictionary/no-op holders (no Unity in their ctors); the resolution-path ctor
+    // dereferences these immediately (CreateBackgroundId / CreateManager / UnityEventAgent wiring).
+    public DataMgr GetDataMgr() => _data ??= new DataMgr();
     public GameObjMgr GetGameObjMgr() => _gameObj;
-    public PrefabMgr GetPrefabMgr() => _prefab;
-    public InputMgr GetInputMgr() => _input;
-    public BattleControl GetBattleCtrl() => _battleCtrl;
+    public PrefabMgr GetPrefabMgr() => _prefab ??= new PrefabMgr();
+    public InputMgr GetInputMgr() => _input ??= new InputMgr();
+    public BattleControl GetBattleCtrl() => _battleCtrl ??= new BattleControl();
     public NetworkUserInfoData GetNetworkUserInfoData() => _netUser;
     public void SetNetworkUserInfoData(NetworkUserInfoData infoData) => _netUser = infoData;
     public Wizard.MailTopTask GetMailTopTask() => null;