Z-order via position.z and reset-to-default for asset properties

- Position is now { x, y, z }; higher z draws on top, ties keep hierarchy order
- Viewport sorts the objects layer deterministically (syncDrawOrder)
- Inspector shows a Z field; asset properties that differ from the schema
  default are marked bold with a reset button (ResetAssetPropertyCommand)
- isModified() helper, unit tests, E2E checks and seed updated

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/editor/panels/Inspector.ts

@@ -1,14 +1,14 @@
-import { RenameAssetCommand, SetAssetPropertyCommand } from '../../core/commands/assetCommands';
+import { RenameAssetCommand, ResetAssetPropertyCommand, SetAssetPropertyCommand } from '../../core/commands/assetCommands';
 import {
   ClearOverrideCommand,
   MoveSceneObjectCommand,
   RenameSceneObjectCommand,
   SetOverrideCommand,
 } from '../../core/commands/sceneObjectCommands';
-import type { PropertyValue } from '../../core/model/Properties';
+import type { Position, PropertyValue } from '../../core/model/Properties';
 import { findAsset, findScene, findSceneObject } from '../../core/model/Project';
 import { schemaFor } from '../../core/properties/PropertySchema';
-import { isOverridden, resolveAssetProps, resolveSceneObjectProps } from '../../core/properties/resolve';
+import { isModified, isOverridden, resolveAssetProps, resolveSceneObjectProps } from '../../core/properties/resolve';
 import { Button, HStack, Label, Panel, ScrollContainer, TextField, Theme, VStack } from '../../ui';
 import { createFieldRow, type FieldRow } from '../inspector/fieldFactory';
 import type { EditorState, Selection } from '../state';
@@ -66,25 +66,32 @@ export class Inspector extends Panel {
     });
     this.body.add(this.labelled('Name', this.nameField));
 
+    // Asset properties: values that differ from the schema default are marked and resettable.
     const values = resolveAssetProps(asset);
     for (const def of schemaFor(asset.type)) {
       let original: PropertyValue | undefined;
-      const row = createFieldRow(def, values[def.key] ?? def.default, {
-        onInput: (value) => {
-          const target = findAsset(this.state.project, assetId);
-          if (!target) return;
-          if (original === undefined) original = target.props[def.key];
-          target.props[def.key] = value;
-          this.state.preview();
+      const row = createFieldRow(
+        def,
+        values[def.key] ?? def.default,
+        {
+          onInput: (value) => {
+            const target = findAsset(this.state.project, assetId);
+            if (!target) return;
+            if (original === undefined) original = target.props[def.key];
+            target.props[def.key] = value;
+            this.state.preview();
+          },
+          onChange: (value) => {
+            const target = findAsset(this.state.project, assetId);
+            if (!target) return;
+            if (original !== undefined) target.props[def.key] = original;
+            original = undefined;
+            this.state.execute(new SetAssetPropertyCommand(assetId, def.key, value));
+          },
         },
-        onChange: (value) => {
-          const target = findAsset(this.state.project, assetId);
-          if (!target) return;
-          if (original !== undefined) target.props[def.key] = original;
-          original = undefined;
-          this.state.execute(new SetAssetPropertyCommand(assetId, def.key, value));
-        },
-      });
+        () => this.state.execute(new ResetAssetPropertyCommand(assetId, def.key)),
+      );
+      row.setModified(isModified(asset, def.key));
       this.fields.set(def.key, row);
       this.body.add(row.row);
     }
@@ -110,10 +117,10 @@ export class Inspector extends Panel {
     assetRow.add(new Button(asset.name, { variant: 'ghost', onClick: () => this.state.select({ kind: 'asset', assetId: asset.id }) }), 1);
     this.body.add(assetRow);
 
-    // Position – belongs to the scene object only.
+    // Position – belongs to the scene object only. Z is the draw order (higher = on top).
     this.body.add(new Label('POSITION', { style: 'title' }));
-    for (const axis of ['x', 'y'] as const) {
-      let original: { x: number; y: number } | undefined;
+    for (const axis of ['x', 'y', 'z'] as const) {
+      let original: Position | undefined;
       const row = createFieldRow({ key: axis, label: axis.toUpperCase(), kind: 'number', default: 0, step: 1 }, object.position[axis], {
         onInput: (value) => {
           const target = this.currentObject(sceneId, objectId);
@@ -169,7 +176,7 @@ export class Inspector extends Panel {
         },
         () => this.state.execute(new ClearOverrideCommand(sceneId, objectId, def.key)),
       );
-      row.setOverridden(isOverridden(object, def.key));
+      row.setModified(isOverridden(object, def.key));
       this.fields.set(def.key, row);
       this.body.add(row.row);
     }
@@ -188,7 +195,10 @@ export class Inspector extends Panel {
       if (!asset) return this.rebuild();
       this.nameField?.setValue(asset.name);
       const values = resolveAssetProps(asset);
-      for (const [key, row] of this.fields) row.setValue(values[key] ?? 0);
+      for (const [key, row] of this.fields) {
+        row.setValue(values[key] ?? 0);
+        row.setModified(isModified(asset, key));
+      }
       return;
     }
     const object = this.currentObject(s.sceneId, s.objectId);
@@ -197,11 +207,12 @@ export class Inspector extends Panel {
     this.nameField?.setValue(object.name);
     this.fields.get('x')?.setValue(object.position.x);
     this.fields.get('y')?.setValue(object.position.y);
+    this.fields.get('z')?.setValue(object.position.z);
     const values = resolveSceneObjectProps(asset, object);
     for (const def of schemaFor(asset.type)) {
       const row = this.fields.get(def.key);
       row?.setValue(values[def.key] ?? def.default);
-      row?.setOverridden(isOverridden(object, def.key));
+      row?.setModified(isOverridden(object, def.key));
     }
   }