fix(Core/Wintergrasp): disband raid groups on battle end (azerothcore#26014)

Co-authored-by: Xfurry <xfurry.cmangos@outlook.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

src/server/game/Battlefield/Battlefield.cpp

@@ -407,6 +407,14 @@ void Battlefield::EndBattle(bool endByTimer)
     OnBattleEnd(endByTimer);
     sScriptMgr->OnBattlefieldWarEnd(this, endByTimer);
 
+    for (uint8 team = 0; team < PVP_TEAMS_COUNT; ++team)
+    {
+        for (ObjectGuid const& guid : Groups[team])
+            if (Group* group = sGroupMgr->GetGroupByGUID(guid.GetCounter()))
+                group->Disband();
+        Groups[team].clear();
+    }
+
     // Reset battlefield timer
     Timer = NoWarBattleTime;
     SendInitWorldStatesToAll();