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/inspector/fieldFactory.ts

@@ -1,6 +1,6 @@
 import type { PropertyValue } from '../../core/model/Properties';
 import type { PropertyDef } from '../../core/properties/PropertySchema';
-import { Button, Checkbox, ColorField, HStack, Label, Menu, NumberField, TextField, Theme, ui, type Widget } from '../../ui';
+import { Button, Checkbox, ColorField, HStack, Label, Menu, NumberField, Spacer, TextField, Theme, ui, type Widget } from '../../ui';
 
 export interface FieldHandlers {
   /** Live value while dragging/typing – apply as a preview, no undo entry. */
@@ -21,10 +21,10 @@ export interface FieldRow {
 }
 
 /** Width of the label column every inspector row aligns to. */
-export const FIELD_LABEL_WIDTH = 64;
+const FIELD_LABEL_WIDTH = 64;
 
 /** One way of resetting or applying a value ("Reset to asset", "Apply to container", …). */
-export interface FieldAction {
+interface FieldAction {
   label: string;
   onSelect: () => void;
 }
@@ -58,7 +58,7 @@ export function createFieldRow(def: PropertyDef, value: PropertyValue, handlers:
   const { row, label } = labelledRow(def.label);
   const field = createField(def, value, handlers);
   row.add(field.widget, field.grow ? 1 : 0);
-  if (!field.grow) row.add(new Label(''), 1);
+  if (!field.grow) row.add(new Spacer(), 1);
 
   const actions: { button: Button; glyph: string; available: FieldActions }[] = [];
   const addActions = (glyph: string, available: FieldActions): void => {
@@ -107,7 +107,7 @@ export function createFieldRow(def: PropertyDef, value: PropertyValue, handlers:
   };
 }
 
-export interface Field {
+interface Field {
   widget: Widget;
   /** Whether the widget should take the remaining row width. */
   grow: boolean;