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/Samples~/Rudder.Unity.Samples.asmdef

@@ -0,0 +1,16 @@
+{
+    "name": "Rudder.Unity.Samples",
+    "rootNamespace": "RudderSdk.Unity.Samples",
+    "references": [
+        "Rudder.Unity"
+    ],
+    "includePlatforms": [],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": false,
+    "precompiledReferences": [],
+    "autoReferenced": false,
+    "defineConstraints": [],
+    "versionDefines": [],
+    "noEngineReferences": false
+}