port(m1): wave 7h — Unity overloads + SDK return types + RoomRoot:UIBase (56->40)

- Resources.LoadAsync(string) non-generic, LayerMask implicit-from-int, Animation
  string indexer.
- SDK return-type fixes: RedShellSDK.MarkConversion/LogEvent return IEnumerator
  (StartCoroutine arg), Packsize.Test() returns bool (!Test()).
- RoomRoot : UIBase (decomp base) so TopBar/Footer's (RoomRoot) casts succeed.

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

SVSim.BattleEngine/Shim/UnityEngine/UnityRuntime.cs

@@ -55,6 +55,7 @@ namespace UnityEngine
         public static T[] LoadAll<T>(string path) where T : Object => new T[0];
         public static Object[] LoadAll(string path) => new Object[0];
         public static ResourceRequest LoadAsync<T>(string path) where T : Object => null;
+        public static ResourceRequest LoadAsync(string path) => null;
         public static void UnloadAsset(Object o) { }
         public static AsyncOperation UnloadUnusedAssets() => null;
     }