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-shared/src/metadata/constants/standard-object.constant.ts

@@ -1838,15 +1838,24 @@ export const STANDARD_OBJECTS = {
       searchVector: {
         universalIdentifier: 'c63e091f-6528-4657-ad2a-b0a158f9e483',
       },
+      subject: {
+        universalIdentifier: 'a8ddbf8c-1137-45d1-b89e-5ffbd83f67c8',
+      },
     },
     indexes: {},
     views: {
       allMessageThreads: {
         universalIdentifier: '20202020-d002-4d02-8d02-ae55a9ba2002',
         viewFields: {
+          subject: {
+            universalIdentifier: 'e5f0d32b-2b6a-47bc-b3bd-f32c96594ec1',
+          },
           messages: {
             universalIdentifier: '20202020-df02-4d02-8d02-ae55a9ba2f01',
           },
+          updatedAt: {
+            universalIdentifier: 'af2c6ac9-7083-4609-8172-d518441f5e9e',
+          },
           createdAt: {
             universalIdentifier: '20202020-df02-4d02-8d02-ae55a9ba2f02',
           },

packages/twenty-shared/src/types/SidePanelPages.ts

@@ -3,7 +3,6 @@ export enum SidePanelPages {
   ViewRecord = 'view-record',
   MergeRecords = 'merge-records',
   UpdateRecords = 'update-records',
-  ViewEmailThread = 'view-email-thread',
   ViewCalendarEvent = 'view-calendar-event',
   EditRichText = 'edit-rich-text',
   Copilot = 'copilot',

packages/twenty-shared/src/types/index.ts

@@ -186,6 +186,7 @@ export type {
   NotesConfiguration,
   FilesConfiguration,
   EmailsConfiguration,
+  EmailThreadConfiguration,
   CalendarConfiguration,
   WorkflowConfiguration,
   WorkflowVersionConfiguration,

packages/twenty-shared/src/types/page-layout/page-layout-widget-configuration.type.ts

@@ -151,6 +151,10 @@ export type EmailsConfiguration = {
   configurationType: 'EMAILS';
 };
 
+export type EmailThreadConfiguration = {
+  configurationType: 'EMAIL_THREAD';
+};
+
 export type CalendarConfiguration = {
   configurationType: 'CALENDAR';
 };
@@ -189,4 +193,5 @@ export type PageLayoutWidgetConfiguration =
   | CalendarConfiguration
   | WorkflowConfiguration
   | WorkflowVersionConfiguration
-  | WorkflowRunConfiguration;
+  | WorkflowRunConfiguration
+  | EmailThreadConfiguration;