fix(UVE): copy content modal error (#34474)

This PR fixes: #34300

### Video


https://github.com/user-attachments/assets/46f95aa6-c3b4-4a77-9b92-84692421ebc7

Author: rjvelazco

core-web/libs/dotcms-models/src/lib/dot-tree-node.model.ts

@@ -4,6 +4,6 @@ export interface DotTreeNode {
     pageId: string;
     relationType: string;
     treeOrder: string;
-    variantId: string;
+    variantId?: string;
     personalization?: string;
 }

core-web/libs/portlets/edit-ema/portlet/src/lib/store/features/editor/withEditor.spec.ts

@@ -7,7 +7,7 @@ import { computed, signal } from '@angular/core';
 import { ActivatedRoute, Router } from '@angular/router';
 
 import { DotPropertiesService } from '@dotcms/data-access';
-import { DotDeviceListItem } from '@dotcms/dotcms-models';
+import { DEFAULT_VARIANT_ID, DotDeviceListItem } from '@dotcms/dotcms-models';
 import { UVE_MODE } from '@dotcms/types';
 import { WINDOW } from '@dotcms/utils';
 import { mockDotDevices, seoOGTagsMock } from '@dotcms/utils-testing';
@@ -930,15 +930,15 @@ describe('withEditor', () => {
             it('should return the current TreeNode with variantId from store.$variantId()', () => {
                 const { container, contentlet } = ACTION_PAYLOAD_MOCK;
 
-                // When variantId is not set in pageParams, $variantId() returns empty string
+                // When variantId is not set in pageParams, $variantId() returns DEFAULT_VARIANT_ID
                 expect(store.getCurrentTreeNode(container, contentlet)).toEqual({
                     containerId: 'container-identifier-123',
                     contentId: 'contentlet-identifier-123',
                     pageId: '123',
                     personalization: 'dot:persona:dot:persona',
                     relationType: 'uuid-123',
                     treeOrder: '-1',
-                    variantId: '' // Uses store.$variantId() which comes from pageParams()?.variantId ?? ''
+                    variantId: DEFAULT_VARIANT_ID
                 });
             });
 

core-web/libs/portlets/edit-ema/portlet/src/lib/store/features/withPageContext.ts

@@ -2,7 +2,7 @@ import { signalStoreFeature, type, withComputed } from '@ngrx/signals';
 
 import { computed, Signal } from '@angular/core';
 
-import { DotExperimentStatus } from '@dotcms/dotcms-models';
+import { DEFAULT_VARIANT_ID, DotExperimentStatus } from '@dotcms/dotcms-models';
 import { UVE_MODE } from '@dotcms/types';
 
 import { withFlags } from './flags/withFlags';
@@ -79,7 +79,7 @@ export function withPageContext() {
                     $hasAccessToEditMode,
                     $languageId: computed(() => viewAs()?.language?.id || 1),
                     $pageURI: computed(() => page()?.pageURI ?? ''),
-                    $variantId: computed(() => pageParams()?.variantId ?? ''),
+                    $variantId: computed(() => pageParams()?.variantId ?? DEFAULT_VARIANT_ID),
                     $canEditPage: computed(() => $hasAccessToEditMode() && $isEditMode())
                 } satisfies PageContextComputed;
             }