Disable reset to default when custom tab or widget (#19814)

## Context
"Reset to default" action is rejected by the backend for custom entities
because there is no "default" concept for them

## Implementation
Grey out the Reset to default action on record page-layout tabs and
widgets when the entity either has no applicationId yet (unsaved draft —
previously slipped through the existing check), or belongs to the
workspace custom application.

<img width="926" height="370" alt="Screenshot 2026-04-17 at 18 50 31"
src="https://github.com/user-attachments/assets/c7c163f4-17a6-4b69-a66d-90f9085d27a2"
/>

packages/twenty-front/src/testing/mock-data/widget-configurations.ts

@@ -123,6 +123,7 @@ export const createTestWidget = (
 ): PageLayoutWidget => ({
   __typename: 'PageLayoutWidget',
   id: 'widget-1',
+  applicationId: 'test-application-id',
   pageLayoutTabId: 'tab-1',
   title: 'Test Widget',
   type: WidgetType.GRAPH,