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/helpers/memoryPlanStore.ts

@@ -1,29 +1,3 @@
-import type { PlanStateStore } from '../../src/scenario/engine/IndexedDbPlanStore.js';
-
-/**
- * In-memory PlanStateStore that survives across RudderClient instances — lets a
- * test simulate a page reload: drive scenario A on one client, construct a fresh
- * client sharing the same `backing`, call `scenarios.restore()`, and assert the
- * run resumed mid-DAG.
- */
-export function createMemoryPlanStore(backing: { value: string | null } = { value: null }): PlanStateStore {
-  return {
-    get state() {
-      return backing.value;
-    },
-    set state(v: string | null) {
-      backing.value = v;
-    },
-    async load() {
-      /* state already in `backing` */
-    },
-    async save(s: string | null) {
-      backing.value = s;
-    },
-  };
-}
-
-/** Deterministic, collision-free crypto.randomUUID() stub for scenario run IDs. */
 export function stubDeterministicUuid(): void {
   let n = 0;
   const existing = (globalThis as { crypto?: Crypto }).crypto ?? ({} as Crypto);