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

test/e2e/storage.e2e.test.ts

@@ -8,7 +8,7 @@ function makeClient(): RudderClient {
     baseUrl: 'https://api.test.rudder.build',
     projectKey: 'test-project',
     tokenStore: createFakeTokenStore(),
-    runtime: { planStateStore: null, loginEvent: null },
+    runtime: { loginEvent: null },
   });
 }