Server-side scenario execution: effects client replaces local engine

- client.Effects: typed effects + completion methods posting scenario callbacks
- client.Scenario reduced to TriggerAsync
- pending polling via Update() pump: 30s heartbeat + wait-deadline checks
- local engine, plan persistence (IPlanStateStore) and resume removed
- RealtimeService and realtime transports removed (relay never deployed)
- dead IPlanScheduler leftover removed
- models regenerated from openapi (ExecutionPlan/BoundaryNode gone, PendingEffect added)

BattlePass/AddBattlePassXpResponse.cs

@@ -1,6 +1,5 @@
 // Code generated by apigen. DO NOT EDIT.
 using Newtonsoft.Json;
-using RudderSdk.Core.Models;
 
 namespace RudderSdk.Core.Models.BattlePass;
 
@@ -15,9 +14,6 @@ public class AddBattlePassXpResponse
     [JsonProperty("maxLevel")]
     public bool? MaxLevel { get; set; }
 
-    [JsonProperty("plan")]
-    public ExecutionPlan? Plan { get; set; }
-
     [JsonProperty("xp")]
     public long? Xp { get; set; }