Add email thread widget and message thread record page layout (#19351)

## Summary
- Move email thread display from side panel to a dedicated record page
with a new `EMAIL_THREAD` widget type
- Add message thread as a standard object with page layout, subject
field, and backfill command
- Add reply-to-email command menu item for message thread records
- Remove old side panel message thread components in favor of the new
widget-based approach

## Type fixes
- Add `EMAIL_THREAD` to `WidgetConfigurationType`, `WidgetType`, and all
configuration/validator maps
- Create `EmailThreadConfigurationDTO` and shared
`EmailThreadConfiguration` type
- Register EMAIL_THREAD in widget type validators, configuration
resolvers, and standard widget mappings

## Test plan
- [ ] Verify message thread record pages render with the email thread
widget
- [ ] Verify email thread preview navigates to the record page instead
of opening side panel
- [ ] Verify reply-to-email command appears for message thread records
- [ ] Verify typecheck passes for both twenty-front and twenty-server
- [ ] Run existing test suites to check for regressions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/twenty-front/src/modules/page-layout/constants/DefaultMessageThreadRecordPageLayout.ts

@@ -0,0 +1,61 @@
+import { DEFAULT_MESSAGE_THREAD_RECORD_PAGE_LAYOUT_ID } from '@/page-layout/constants/DefaultMessageThreadRecordPageLayoutId';
+import { type PageLayout } from '@/page-layout/types/PageLayout';
+import {
+  PageLayoutTabLayoutMode,
+  PageLayoutType,
+  WidgetConfigurationType,
+  WidgetType,
+} from '~/generated-metadata/graphql';
+
+export const DEFAULT_MESSAGE_THREAD_RECORD_PAGE_LAYOUT: PageLayout = {
+  __typename: 'PageLayout',
+  id: DEFAULT_MESSAGE_THREAD_RECORD_PAGE_LAYOUT_ID,
+  name: 'Default Message Thread Layout',
+  type: PageLayoutType.RECORD_PAGE,
+  objectMetadataId: null,
+  createdAt: new Date().toISOString(),
+  updatedAt: new Date().toISOString(),
+  deletedAt: null,
+  tabs: [
+    {
+      __typename: 'PageLayoutTab',
+      applicationId: '',
+      id: 'message-thread-tab-home',
+      title: 'Home',
+      icon: 'IconHome',
+      position: 100,
+      layoutMode: PageLayoutTabLayoutMode.VERTICAL_LIST,
+      pageLayoutId: DEFAULT_MESSAGE_THREAD_RECORD_PAGE_LAYOUT_ID,
+      isOverridden: false,
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+      deletedAt: null,
+      widgets: [
+        {
+          __typename: 'PageLayoutWidget',
+          id: 'message-thread-widget-email-thread',
+          pageLayoutTabId: 'message-thread-tab-home',
+          title: 'Thread',
+          type: WidgetType.EMAIL_THREAD,
+          objectMetadataId: null,
+          gridPosition: {
+            __typename: 'GridPosition',
+            row: 0,
+            column: 0,
+            rowSpan: 12,
+            columnSpan: 12,
+          },
+          configuration: {
+            __typename: 'FieldsConfiguration',
+            configurationType: WidgetConfigurationType.FIELDS,
+            viewId: null,
+          },
+          isOverridden: false,
+          createdAt: new Date().toISOString(),
+          updatedAt: new Date().toISOString(),
+          deletedAt: null,
+        },
+      ],
+    },
+  ],
+};

packages/twenty-front/src/modules/page-layout/constants/DefaultMessageThreadRecordPageLayoutId.ts

@@ -0,0 +1,2 @@
+export const DEFAULT_MESSAGE_THREAD_RECORD_PAGE_LAYOUT_ID =
+  'default-message-thread-page-layout';