feat(push): smart push queueing with page-visibility fast path and app-ping/pong fallback

server/ws-types.ts

@@ -8,6 +8,8 @@ export const WS = {
   SET_PERMISSION_MODE: 'set-permission-mode',
   SET_MODEL: 'set-model',
   PLAN_RESPONSE: 'plan-response',
+  PAGE_VISIBILITY: 'page-visibility',
+  APP_PONG: 'app-pong',
   // Server → Client
   SESSION_STATE: 'session-state',
   SESSION_CREATED: 'session-created',
@@ -39,6 +41,8 @@ export const WS = {
   REVIEW_ENDED: 'review-ended',
   // Task Progress
   TASK_STATE: 'task-state',
+  // Push notification coordination
+  APP_PING: 'app-ping',
 } as const;
 
 export type WsType = typeof WS[keyof typeof WS];