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/database/repos/page/page.repo.ts

@@ -173,9 +173,23 @@ export class PageRepo {
       .returning(this.baseFields)
       .executeTakeFirst();
 
+    // Enrich the event with a thin node snapshot (variant A) so the WS tree
+    // listener can broadcast `addTreeNode` without re-reading the DB. `result`
+    // already comes from `returning(this.baseFields)`, so no extra query.
     this.eventEmitter.emit(EventName.PAGE_CREATED, {
       pageIds: [result.id],
       workspaceId: result.workspaceId,
+      pages: [
+        {
+          id: result.id,
+          slugId: result.slugId,
+          title: result.title,
+          icon: result.icon,
+          position: result.position,
+          spaceId: result.spaceId,
+          parentPageId: result.parentPageId,
+        },
+      ],
     });
 
     return result;
@@ -266,6 +280,25 @@ export class PageRepo {
   ): Promise<void> {
     const currentDate = new Date();
 
+    // Read the root snapshot up front so PAGE_SOFT_DELETED can carry it without
+    // a post-commit DB read (variant A). Only the root of the deleted subtree is
+    // needed for the tree broadcast — the client `treeModel.remove` drops all
+    // descendants, so we don't snapshot/broadcast every descendant.
+    const rootSnapshot = await this.db
+      .selectFrom('pages')
+      .select([
+        'id',
+        'slugId',
+        'title',
+        'icon',
+        'position',
+        'spaceId',
+        'parentPageId',
+      ])
+      .where('id', '=', pageId)
+      .where('deletedAt', 'is', null)
+      .executeTakeFirst();
+
     const descendants = await this.db
       .withRecursive('page_descendants', (db) =>
         db
@@ -305,6 +338,21 @@ export class PageRepo {
       this.eventEmitter.emit(EventName.PAGE_SOFT_DELETED, {
         pageIds: pageIds,
         workspaceId,
+        // Root-only snapshot: one `deleteTreeNode` is enough, the client removes
+        // the whole subtree. Skip if the root vanished between the two reads.
+        pages: rootSnapshot
+          ? [
+              {
+                id: rootSnapshot.id,
+                slugId: rootSnapshot.slugId,
+                title: rootSnapshot.title,
+                icon: rootSnapshot.icon,
+                position: rootSnapshot.position,
+                spaceId: rootSnapshot.spaceId,
+                parentPageId: rootSnapshot.parentPageId,
+              },
+            ]
+          : [],
       });
     }
   }
@@ -313,7 +361,7 @@ export class PageRepo {
     // First, check if the page being restored has a deleted parent
     const pageToRestore = await this.db
       .selectFrom('pages')
-      .select(['id', 'parentPageId'])
+      .select(['id', 'parentPageId', 'spaceId'])
       .where('id', '=', pageId)
       .executeTakeFirst();
 
@@ -372,6 +420,10 @@ export class PageRepo {
     this.eventEmitter.emit(EventName.PAGE_RESTORED, {
       pageIds: pageIds,
       workspaceId: workspaceId,
+      // spaceId lets the WS listener send a space-scoped refetchRootTreeNodeEvent.
+      // Restore can re-attach a whole subtree, so a root refetch is simpler and
+      // more robust than N pointwise addTreeNode events.
+      spaceId: pageToRestore.spaceId,
     });
   }