Server-side scenario execution: new Rudder.Core.dll, realtime/planstore glue removed

- Rudder.Core.dll rebuilt from csharp-sdk effects rewrite (96,768 bytes)
- Realtime/ adapters, UnityRealtimeTransportFactory, UnityPlanStateStore,
  UnityPlanScheduler, WebGL jslib and RealtimeUrl config deleted (with .meta)
- Scenarios sample rewired to client.Effects; samples login path updated
- AGENTS.md/README/CHANGELOG/package docs + agent skill updated; realtime.md skill doc removed

Packages/rudder.sdk/Runtime/Sources/RudderConfiguration.cs

@@ -11,9 +11,6 @@ namespace RudderSdk.Unity
     [Tooltip("API base URL, e.g. https://api.rudder.build.")]
     public string BaseUrl = "https://api.rudder.build";
 
-    [Tooltip("Realtime websocket URL. The relay is not deployed yet; set this only once it is.")]
-    public string RealtimeUrl = "wss://api.rudder.build/api/realtime/ws";
-
     [Tooltip("HTTP request timeout in seconds.")]
     [Min(1)]
     public int TimeoutSeconds = 10;