Fix findUsages/undo/node-lookup bugs, split Viewport and Editor, share command and inspector helpers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/model/Project.ts

@@ -1,4 +1,4 @@
-import type { Asset, SceneAsset } from './Asset';
+import type { Asset, ContainerAsset, SceneAsset } from './Asset';
 import { isSceneAsset } from './Asset';
 import type { SceneObject } from './SceneObject';
 
@@ -32,21 +32,32 @@ export function listScenes(project: Project): SceneAsset[] {
   return project.assets.filter(isSceneAsset);
 }
 
+/**
+ * Everything that holds placed objects. Container assets do so just like scenes: their
+ * `objects` are the template a placed container is instantiated from. Anything that walks
+ * "all placed objects" has to cover both, or it silently skips the templates.
+ */
+export type ObjectHolder = SceneAsset | ContainerAsset;
+
+export function objectHolders(project: Project): ObjectHolder[] {
+  return project.assets.filter((a): a is ObjectHolder => a.type === 'scene' || a.type === 'container');
+}
+
 export interface SceneObjectRef {
-  scene: SceneAsset;
+  holder: ObjectHolder;
   object: SceneObject;
 }
 
-/** Objects of all scenes that satisfy `predicate`, each with the scene it belongs to. */
-export function sceneObjectsWhere(project: Project, predicate: (object: SceneObject) => boolean): SceneObjectRef[] {
+/** Objects of all scenes and container templates that satisfy `predicate`, each with its holder. */
+export function objectsWhere(project: Project, predicate: (object: SceneObject) => boolean): SceneObjectRef[] {
   const result: SceneObjectRef[] = [];
-  for (const scene of listScenes(project)) {
-    for (const object of scene.objects) if (predicate(object)) result.push({ scene, object });
+  for (const holder of objectHolders(project)) {
+    for (const object of holder.objects) if (predicate(object)) result.push({ holder, object });
   }
   return result;
 }
 
-/** Every placed instance of an asset, across all scenes. */
+/** Every placed instance of an asset, in scenes and in container templates alike. */
 export function findUsages(project: Project, assetId: string): SceneObjectRef[] {
-  return sceneObjectsWhere(project, (o) => o.assetId === assetId);
+  return objectsWhere(project, (o) => o.assetId === assetId);
 }