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;
     }

SVSim.BattleEngine/Shim/UnityEngine/UnityShim.cs

@@ -51,7 +51,7 @@ namespace UnityEngine
     public struct Ray { public Ray(Vector3 origin, Vector3 dir) { this.origin = origin; this.direction = dir; } public Vector3 origin; public Vector3 direction; public Vector3 GetPoint(float d) => origin; }
     public struct RaycastHit { public Vector3 point; public Vector3 normal; public float distance; public Collider collider; public Transform transform; public GameObject gameObject; }
     public struct RaycastHit2D { public Vector3 point; public Vector3 normal; public float distance; public Collider2D collider; public Transform transform; public static implicit operator bool(RaycastHit2D hit) => hit.collider != null; }
-    public struct LayerMask { public int value; public static int NameToLayer(string n) => 0; public static string LayerToName(int layer) => ""; public static implicit operator int(LayerMask m) => m.value; }
+    public struct LayerMask { public int value; public static int NameToLayer(string n) => 0; public static string LayerToName(int layer) => ""; public static implicit operator int(LayerMask m) => m.value; public static implicit operator LayerMask(int v) => new LayerMask { value = v }; }
 
     // ---- core object model ----
     public class Object
@@ -301,7 +301,7 @@ namespace UnityEngine
     public partial class Sprite : Object { public Rect rect => default; public Texture2D texture => null; public static Sprite Create(Texture2D t, Rect r, Vector2 pivot) => null; }
     public partial class Shader : Object { public static Shader Find(string n) => null; public bool isSupported => true; }
     public class AnimationClip : Object { public float length => 0f; public string name { get; set; } public float frameRate => 0f; }
-    public partial class Animation : Component, IEnumerable { public AnimationClip clip { get; set; } public bool isPlaying => false; public void Play() { } public void Play(string n) { } public void Stop() { } public IEnumerator GetEnumerator() { yield break; } }
+    public partial class Animation : Component, IEnumerable { public AnimationClip clip { get; set; } public bool isPlaying => false; public void Play() { } public void Play(string n) { } public void Stop() { } public IEnumerator GetEnumerator() { yield break; } public AnimationState this[string name] => null; }
     public class Animator : Component
     {
         public void SetTrigger(string n) { } public void SetTrigger(int id) { }