Improve editor placement and selection workflows (#543)

* feat: expose accepted canvas node selections

* feat(editor): replace bulk delete alert with dialog

* fix(editor): allow immediate selection after opening placement

* feat(spawn): preview model during placement

* feat(editor): add cross-project selection clipboard

* fix(editor): harden placement and clipboard previews

* fix(editor): preserve carried clipboard state

* fix(editor): replace active paste drafts safely

packages/core/src/events/bus.ts

@@ -276,6 +276,12 @@ type RoomPresetEvents = {
 }
 
 type SelectionEvents = {
+  /**
+   * A node click accepted by an editor canvas selection path after proxy and
+   * phase routing. Hosts can react to the user's 2D/3D selection intent
+   * without treating programmatic selection changes as canvas clicks.
+   */
+  'selection:canvas-node-click': AnyNode
   /**
    * "Reveal this node" intent — the editor's node action menu emits it with the
    * selected node; whoever owns the node's catalog/panel (host browser, a