feat(tree): server-authoritative realtime tree updates

The sidebar page tree only updated on other clients when a change was made
via the UI tree, in an open tab, within a ~50ms client relay window — API/MCP/
AI/import changes never propagated. Move the source of truth to the server.

Server:
- Enrich PageEvent with thin TreeNodeSnapshot(s) so the WS listener never reads
  the DB (avoids the in-transaction visibility race). insertPage fills the
  create snapshot from its returning() row; removePage ships only the deleted
  subtree ROOT (client treeModel.remove drops descendants); restorePage carries
  spaceId.
- New PAGE_MOVED event from movePage with old/new parent + position + snapshot
  (generic PAGE_UPDATED stays for content/rename).
- WsService.emitTreeEvent mirrors emitCommentEvent (per-space restriction gate:
  spaceHasRestrictions -> hasRestrictedAncestor -> broadcastToAuthorizedUsers);
  author NOT excluded so non-UI creators see their own page (receiver is
  idempotent).
- WsTreeService.broadcastPageCreated/Deleted/Moved + broadcastRefetchRoot;
  new PageWsListener (create/delete/move/restore) registered in WsModule.

Client:
- Remove the client relay (emit + setTimeout(50)) from create/move/delete;
  keep optimistic local updates. Make the optimistic create insert id-idempotent
  (find-then-skip) so the now-fast server addTreeNode broadcast can't race it
  into a duplicate row. addTreeNode inserts by fractional position among loaded
  siblings (consistent order across clients).

Restore uses refetchRootTreeNodeEvent (robust for subtree re-attach). Rename/icon
updateOne and cross-space move realtime are deferred (commented as follow-ups).

Implements docs/backlog/realtime-tree-server-authoritative.md.

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

apps/server/src/core/page/page.controller.ts

@@ -724,7 +724,11 @@ export class PageController {
     @AuthUser() user: User,
     @AuthProvenance() provenance: AuthProvenanceData,
   ) {
-    const movedPage = await this.pageRepo.findById(dto.pageId);
+    // includeHasChildren so movePage's PAGE_MOVED snapshot carries an accurate
+    // hasChildren — receivers need it to keep the moved node's chevron correct.
+    const movedPage = await this.pageRepo.findById(dto.pageId, {
+      includeHasChildren: true,
+    });
     if (!movedPage) {
       throw new NotFoundException('Moved page not found');
     }

apps/server/src/core/page/services/page.service.ts

@@ -887,6 +887,35 @@ export class PageService {
       },
       dto.pageId,
     );
+
+    // The generic PAGE_UPDATED emitted by updatePage above is intentionally NOT
+    // used to drive the tree `moveTreeNode` broadcast: it also fires on rename /
+    // content-save and carries neither oldParentId nor the new position. Emit a
+    // dedicated PAGE_MOVED so the WS listener can build a precise moveTreeNode
+    // without a DB read (variant A: snapshot in the event).
+    //
+    // `parentPageId` is `undefined` when only the position changed (same
+    // parent); resolve it back to the page's actual parent for the snapshot.
+    const newParentPageId =
+      parentPageId === undefined ? movedPage.parentPageId : parentPageId;
+
+    this.eventEmitter.emit(EventName.PAGE_MOVED, {
+      workspaceId: movedPage.workspaceId,
+      oldParentId: movedPage.parentPageId ?? null,
+      // `hasChildren` is selected by findById({ includeHasChildren: true }) in
+      // the controller; it isn't on the base Page type, hence the cast.
+      hasChildren:
+        (movedPage as Page & { hasChildren?: boolean }).hasChildren ?? false,
+      node: {
+        id: movedPage.id,
+        slugId: movedPage.slugId,
+        title: movedPage.title,
+        icon: movedPage.icon,
+        position: dto.position,
+        spaceId: movedPage.spaceId,
+        parentPageId: newParentPageId ?? null,
+      },
+    });
   }
 
   async getPageBreadCrumbs(childPageId: string) {