chore(battle-engine M13): drop unused using + complete shim comment (review polish)

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

SVSim.BattleEngine.Tests/HeadlessFixture.cs

@@ -209,7 +209,8 @@ namespace SVSim.BattleEngine.Tests
             // _netUser null (no lazy init, unlike the other GodObject getters). Seed a no-op instance
             // whose _selfInfo carries just "fieldId" (GetFieldId reads _selfInfo["fieldId"]); field id 1
             // == ForestField, a valid background. Nothing here drives game state — it only satisfies the
-            // network mgr's background lookup so a single-battle-only SingleBattleMgr never needs.
+            // network mgr's background lookup, a background lookup the single-battle path
+            // (`SingleBattleMgr`) never performs.
             var netUser = new NetworkUserInfoData();
             netUser.SetSelfInfo(
                 new System.Collections.Generic.Dictionary<string, object> { ["fieldId"] = 1 },

SVSim.BattleEngine/Rng/HeadlessNetworkBattleMgr.cs

@@ -1,4 +1,3 @@
-using Wizard;
 using Wizard.BattleMgr;
 
 namespace SVSim.BattleEngine.Rng