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/editor/graph/NodePalette.ts

@@ -7,6 +7,7 @@ const CATEGORY_ORDER: NodeCategory[] = ['event', 'flow', 'variable', 'data', 'ac
 export class NodePalette extends Popup {
   private readonly search: TextField;
   private readonly list = new ListView();
+  private readonly scroll = new ScrollContainer();
   private filtered: NodeDef[] = [];
   /** Guards against a second pick per opening (e.g. Enter and a row click racing). */
   private picked = false;
@@ -25,10 +26,9 @@ export class NodePalette extends Popup {
       },
     });
     this.content.add(this.search);
-    const scroll = new ScrollContainer();
-    scroll.minHeight = 260;
-    scroll.setContent(this.list);
-    this.content.add(scroll, 1);
+    this.scroll.minHeight = 260;
+    this.scroll.setContent(this.list);
+    this.content.add(this.scroll, 1);
     this.list.rowHeight = Theme.rowHeight - 2;
     this.list.emptyText = 'No matching node';
     this.list.onSelect = (id) => {
@@ -50,7 +50,7 @@ export class NodePalette extends Popup {
       .filter((d) => !query || d.label.toLowerCase().includes(query) || d.type.toLowerCase().includes(query) || d.description.toLowerCase().includes(query))
       .sort((a, b) => CATEGORY_ORDER.indexOf(a.category) - CATEGORY_ORDER.indexOf(b.category) || a.label.localeCompare(b.label));
     this.list.setItems(this.filtered.map((d) => ({ id: d.type, label: d.label, hint: d.category })));
-    (this.content.items[1] as ScrollContainer | undefined)?.relayoutContent();
+    this.scroll.relayoutContent();
   }
 
   private pick(def: NodeDef): void {