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)

Services/Effects/QuestEffect.cs

@@ -0,0 +1,62 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+
+namespace RudderSdk.Core;
+
+/// <summary>
+/// A scenario quest node. Report objective progress; the server auto-completes
+/// the node once every objective is satisfied.
+/// </summary>
+public sealed class QuestEffect
+{
+    private readonly EffectHandle _handle;
+
+    internal QuestEffect(EffectHandle handle) => _handle = handle;
+
+    /// <summary>Run id.</summary>
+    public string RunId => _handle.RunId;
+
+    /// <summary>Scenario id.</summary>
+    public string ScenarioId => _handle.ScenarioId;
+
+    /// <summary>Node id.</summary>
+    public string NodeId => _handle.NodeId;
+
+    /// <summary>Quest name from the node data.</summary>
+    public string Name => _handle.Get("name", string.Empty);
+
+    /// <summary>Objective definitions from the node data.</summary>
+    public IReadOnlyList<JObject> Objectives
+    {
+        get
+        {
+            if (_handle.Data["objectives"] is not JArray array)
+                return Array.Empty<JObject>();
+
+            var list = new List<JObject>(array.Count);
+            foreach (var item in array)
+            {
+                if (item is JObject obj)
+                    list.Add(obj);
+            }
+
+            return list;
+        }
+    }
+
+    /// <summary>Node data payload.</summary>
+    public JObject Data => _handle.Data;
+
+    /// <summary>Reads a typed value from the node data.</summary>
+    public T Get<T>(string key, T defaultValue = default!) => _handle.Get(key, defaultValue);
+
+    /// <summary>Reports progress toward an objective via <c>POST /sdk/v1/scenarios/counter</c>.</summary>
+    public Task ReportProgressAsync(string objectiveId, long amount = 1, CancellationToken cancellationToken = default)
+        => _handle.ReportProgressAsync(objectiveId, amount, cancellationToken);
+
+    /// <summary>Reports progress toward an objective (fire-and-forget).</summary>
+    public void ReportProgress(string objectiveId, long amount = 1) => _handle.ReportProgress(objectiveId, amount);
+}