fix: prevent default object re-selection in relation field form (#17313)

Fixes #17111

### Problem
When creating a Relation field, after deselecting the pre-selected
default object (e.g., Company) and selecting a different object (e.g.,
Opportunity), both objects would end up being selected, showing "2
Objects" instead of just the newly selected one.

### Root Cause
The `initialMorphRelationsObjectMetadataIds` array was being recreated
on every component render, causing react-hook-form's `Controller` to
treat the `defaultValue` prop as a new value and re-apply it after user
changes.

### Solution
1. **Memoized the initial value**: Used `useMemo` to ensure
`initialMorphRelationsObjectMetadataIds` has a stable reference across
renders
2. **Added initialization guard**: Used `useEffect` with a `useRef` flag
to ensure the default value is only set once during component mount
3. **Maintained Controller defaultValue**: Kept the `defaultValue` prop
on the Controller, which now works correctly with the stable memoized
value

### Changes
- `SettingsDataModelFieldRelationForm.tsx`: Added memoization and
initialization guard to prevent default value re-application

---------

Co-authored-by: Etienne <45695613+etiennejouan@users.noreply.github.com>

packages/twenty-front/src/modules/settings/data-model/fields/forms/morph-relation/components/SettingsDataModelFieldRelationForm.tsx

@@ -17,6 +17,7 @@ import { SettingsTextInput } from '@/ui/input/components/SettingsTextInput';
 import { useIsMobile } from '@/ui/utilities/responsive/hooks/useIsMobile';
 import styled from '@emotion/styled';
 import { useLingui } from '@lingui/react/macro';
+import { useMemo } from 'react';
 import { isDefined } from 'twenty-shared/utils';
 import { RelationType } from '~/generated-metadata/graphql';
 
@@ -114,10 +115,14 @@ export const SettingsDataModelFieldRelationForm = ({
       relationType: initialRelationType,
     });
 
-  const initialMorphRelationsObjectMetadataIds =
-    initialRelationObjectMetadataItems.map(
-      (relationObjectMetadataItem) => relationObjectMetadataItem.id,
-    );
+  const initialMorphRelationsObjectMetadataIds = useMemo(
+    () =>
+      initialRelationObjectMetadataItems.map(
+        (relationObjectMetadataItem) => relationObjectMetadataItem.id,
+      ),
+    [initialRelationObjectMetadataItems],
+  );
+
   const isMobile = useIsMobile();
 
   return (