fix(offline-sync): bridge collaborative tree updates across processes via Redis

In 2-process deployments (COLLAB_URL set) the standalone collab process runs
Hocuspocus onStoreDocument, which emits PAGE_UPDATED with a treeUpdate snapshot
on a collaborative rename. But CollabAppModule has no WsModule, so PageWsListener
(the broadcaster) only exists in the API process — the collab-originated tree
update never reached clients, and other users' sidebars/breadcrumbs went stale.

Bridge it over Redis pub/sub with the API process as the single broadcast
authority:

- PageTreeBridgePublisher (registered ONLY in CollabAppModule) listens for
  PAGE_UPDATED and, when a treeUpdate snapshot is present, publishes it to the
  collab:tree-update channel. Gated exactly like PageWsListener so content-only
  saves never publish noise.
- PageTreeBridgeSubscriber (registered in WsModule, API process) subscribes on a
  dedicated duplicated connection and re-broadcasts each snapshot through
  WsTreeService.broadcastPageUpdated — the same restriction-aware emitTreeEvent
  path, so authorization is preserved.

Double-broadcast is prevented by module placement: the publisher lives only in
the standalone collab process's root module, so in single-process mode it is
never loaded and the local PageWsListener stays the sole broadcaster.

The bridge is optional and fail-safe: publish errors, malformed payloads,
broadcast rejections, an unlistened 'error' on the subscriber connection, and a
subscribe() failure at boot are all caught and logged, never crashing or blocking
the process. NOTE: assumes a single API broadcaster; horizontal API scaling would
need a consumer-group/leader-election instead of fan-out pub/sub.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/ws/ws.module.ts

@@ -3,12 +3,19 @@ import { WsGateway } from './ws.gateway';
 import { WsService } from './ws.service';
 import { WsTreeService } from './ws-tree.service';
 import { PageWsListener } from './listeners/page-ws.listener';
+import { PageTreeBridgeSubscriber } from './listeners/page-tree-bridge.subscriber';
 import { TokenModule } from '../core/auth/token.module';
 
 @Global()
 @Module({
   imports: [TokenModule],
-  providers: [WsGateway, WsService, WsTreeService, PageWsListener],
+  providers: [
+    WsGateway,
+    WsService,
+    WsTreeService,
+    PageWsListener,
+    PageTreeBridgeSubscriber,
+  ],
   exports: [WsGateway, WsService, WsTreeService],
 })
 export class WsModule {}