Exiles Reach (ship): replace boundary-evade with a distance leash for the sparring clone

The SetBoundary approach made the sparring partner evade back to home with a
straight spline, clipping through the boat hull. Use a distance leash in
UpdateAI instead: stop chasing past 15y and walk back on the ship geometry.

src/server/scripts/ExilesReach/exiles_reach_north_sea.cpp

@@ -214,6 +214,25 @@ struct npc_exiles_reach_ship_166583_160664 : public ScriptedAI
 {
     npc_exiles_reach_ship_166583_160664(Creature* creature) : ScriptedAI(creature) {}
 
+    void SetLeashPosition(Position const& pos) { _leashPosition = pos; _leashSet = true; }
+
+    void UpdateAI(uint32 diff) override
+    {
+        if (Unit* victim = me->GetVictim())
+        {
+            // Stay on the boat: if the sparring partner gets dragged past the
+            // deck edge, stop chasing and walk back on the ship's geometry
+            // (avoids the boundary-evade spline that clips through the hull).
+            if (_leashSet && me->GetDistance(_leashPosition) > 15.0f)
+            {
+                me->AttackStop();
+                me->GetMotionMaster()->MovePoint(0, _leashPosition);
+                return;
+            }
+        }
+        ScriptedAI::UpdateAI(diff);
+    }
+
     void BeFriendly()
     {
         me->AttackStop();
@@ -230,6 +249,9 @@ struct npc_exiles_reach_ship_166583_160664 : public ScriptedAI
         case QUEST_H_STAND_YOUR_GROUND:
             if (Creature* clone = me->SummonPersonalClone(me->GetPosition(), TEMPSUMMON_MANUAL_DESPAWN, 0s, 0U, 0U, player))
             {
+                if (npc_exiles_reach_ship_166583_160664* personalAI = CAST_AI(npc_exiles_reach_ship_166583_160664, clone->AI()))
+                    personalAI->SetLeashPosition(me->GetPosition());
+
                 clone->SetHealth(player->GetHealth());
                 clone->AI()->Talk(0, player);
                 // I'll take my position. Strike first, and strike hard!
@@ -305,6 +327,10 @@ struct npc_exiles_reach_ship_166583_160664 : public ScriptedAI
         else
             me->CastSpell(player, SPELL_JUMP_BEHIND, true);
     }
+
+private:
+    Position _leashPosition;
+    bool _leashSet = false;
 };
 
 void AddSC_exiles_reach_north_sea()