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

src/generated/common.ts

@@ -1,15 +1,5 @@
 // Code generated by apigen. DO NOT EDIT.
 
-export interface BoundaryNode {
-  "callbackUrl"?: string;
-  "enforcement"?: "client" | "server";
-  "enteredAt"?: string;
-  "nodeId"?: string;
-  "sourceHandle"?: string;
-  "sourceNodeId"?: string;
-  "waitDeadline"?: string;
-}
-
 export interface ErrorResponse {
   "code"?: "early_completion" | "forbidden" | "level_not_reached" | "node_not_active" | "objectives_incomplete" | "run_expired" | "run_not_active" | "scenario_not_active" | "unknown_run";
   "error"?: string;
@@ -18,32 +8,6 @@ export interface ErrorResponse {
   "requestId"?: string;
 }
 
-export interface ExecutionPlan {
-  "boundaryNodes"?: BoundaryNode[];
-  "context"?: { [key: string]: unknown };
-  "edges"?: PlanEdge[];
-  "nodes"?: ExecutionPlanNode[];
-  "planId"?: string;
-  "runId"?: string;
-  "scenarioId"?: string;
-  "startNodeId"?: string;
-  "userId"?: string;
-}
-
-export interface ExecutionPlanNode {
-  "data"?: { [key: string]: unknown };
-  "id"?: string;
-  "type"?: string;
-}
-
-export interface PlanEdge {
-  "id"?: string;
-  "source"?: string;
-  "sourceHandle"?: string;
-  "target"?: string;
-  "targetHandle"?: string;
-}
-
 export interface Reward {
   "amount"?: number;
   "currency"?: string;