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/CHANGELOG.md

@@ -1,5 +1,41 @@
 # Changelog
 
+## 0.4.0
+
+Breaking changes, following the Rudder.Core 0.4.0 rework:
+
+- Bundled `Rudder.Core.dll` updated to 0.4.0. The local scenario graph engine
+  is gone. `client.Scenario` is only `TriggerAsync(eventName)`. Pending nodes
+  surface on `client.Effects` (`OnNotification`, `OnStoreOffer`,
+  `OnLeaderboard`, `OnWait`, `OnQuest`, `OnBattlePass`,
+  `OnBattlePassLevel`, `OnScenarioCompleted`, `OnScenarioFailed`).
+- Session types (`NotificationSession`, `StoreOfferSession`, …) are now
+  `*Effect` types. Completion methods: `Done`/`DoneAsync`,
+  `Purchase`/`Decline`, `End`/`Claim`, `ReportProgress`, `LevelUp`.
+- `UnityPlanScheduler` removed together with the core `IPlanScheduler`
+  abstraction and `RudderClientOptions.Scheduler`; the factory no longer
+  wires a scheduler.
+- `UnityPlanStateStore`, `UnityRealtimeTransportFactory`,
+  `Runtime/Sources/Realtime/` websocket adapters, and
+  `Runtime/Plugins/WebGL/RudderWebSocket.jslib` removed together with Core
+  `IPlanStateStore` / `IRealtimeTransport` / `RealtimeService`.
+- `RudderConfiguration.RealtimeUrl` and `RudderUnityClientOptions.RealtimeUrl`
+  removed. `Rudder` no longer disconnects a realtime socket on quit.
+- `Rudder.Update` still pumps `client.Update(Time.deltaTime)` (effects
+  heartbeat and wait-deadline checks).
+- Samples and docs use `Auth.LoginWithDeviceAsync`. Pending effects are
+  fetched after sign-in via the heartbeat; `Scenario.RestoreAsync` /
+  `AuthorizeWithDeviceAsync` are gone.
+- Core model fields are nullable now; samples check
+  `PurchaseResponse.Success != true` instead of `!Success`.
+- Feature sample scenes for authentication, remote config, storage, stores
+  and inventory, leaderboards, and scenarios (`Samples~`).
+- Removed the Cozy Collector example project from the Unity SDK repo.
+- Added `AGENTS.md` with Unity integration rules for coding agents.
+- `Rudder.Initialize()` is now synchronous, takes no arguments, and returns
+  `RudderClient`. Put `Rudder` in a scene with a `RudderConfiguration`.
+  The old `Initialize(RudderConfiguration)` (hidden GameObject) is gone.
+
 ## 0.3.0
 
 Breaking changes, following the Rudder.Core 0.3.0 rework: