Server-side scenario execution: thin effects client replaces local engine

- engine/ (DagWalker, sessions, IndexedDbPlanStore) deleted; server owns the graph
- trigger/callback/counter carry PendingEffect; GET /sdk/v1/scenarios/pending polled
  (30s jittered heartbeat paused on hidden tab + wait-deadline timers)
- client.effects public API unchanged (done/buy/dismiss/end/claim/battlepass/quest)
- planStateStore removed; loginEvent kept; reconcile() makes server the source of truth
- generated models regenerated; skills/README/CHANGELOG updated

skills/rudder-web-sdk/reference/remote-config.md

@@ -56,8 +56,8 @@ already filters inactive configs out and may omit the flag).
 ## Behavior notes
 
 - Warmed at login.
-- Scenario `remote_config_override` nodes patch the local snapshot and fire
-  `client.effects.onConfigChanged({ key })` — the patched value is what
-  `get()` returns afterwards.
+- Scenario `remote_config_override` nodes are applied server-side and do not
+  reach the client. Reload or wait for the config sync poll to observe the
+  patched value via `get()`.
 - Without a `TConfig` type argument, `RemoteConfigShape` defaults to
   `Record<string, unknown>` and `get()` returns `unknown`.