fix(front): allow null subfields in Phones default value so Save enables (#21847)

## Problem

Closes #21780.

When editing a **Phones** field in Settings → Data Model, changing the
**Default Country Code** does not enable the Save button — the form
becomes dirty but never valid, so the change can't be saved.

## Root cause

The settings form validates `defaultValue` with the record-value
`phonesFieldValueSchema`, which requires non-null strings:

```ts
primaryPhoneNumber: z.string(),
primaryPhoneCountryCode: z.string(),
```

But a Phones default value can legitimately have **null** subfields — a
default country code with no default number. The backend normalizes
empty subfields to `null`
(`nullify-empty-phones-default-value.util.ts`), and the shared contract
`FieldMetadataDefaultValuePhones` is `string | null`. So an existing
field whose stored default has `primaryPhoneNumber: null` makes the form
**permanently invalid**: changing the country code preserves the null
number → `isValid` stays `false` → `canSave = isDirty && isValid` keeps
Save disabled.

The sibling **address** field doesn't have this bug because
`addressFieldValueSchema` already makes every subfield `.nullable()`.
Phones was simply inconsistent.

## Fix

Add a dedicated `phonesFieldDefaultValueSchema` with nullable subfields
(mirroring the address pattern and matching
`FieldMetadataDefaultValuePhones`) and use it in the Phones settings
form. The stricter record-value `phonesFieldValueSchema` is left
untouched, so record input/persistence/empty-checks are unaffected.

## Test plan

- [x] Unit test covering the partial-null default value (and asserting
the record-value schema still rejects it)
- [x] `nx typecheck twenty-front` clean
- [x] `nx lint:diff-with-main twenty-front` clean
- Manual: open a Phones field, set a Default Country Code and save,
re-open, change the country code → Save now enables.

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

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Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

packages/twenty-front/src/modules/object-record/record-field/ui/validation-schemas/__tests__/phonesFieldDefaultValueSchema.test.ts

@@ -0,0 +1,27 @@
+import { phonesFieldDefaultValueSchema } from '@/object-record/record-field/ui/validation-schemas/phonesFieldDefaultValueSchema';
+import { phonesFieldValueSchema } from '@/object-record/record-field/ui/validation-schemas/phonesFieldValueSchema';
+
+describe('phonesFieldDefaultValueSchema', () => {
+  it('should accept a fully populated default value', () => {
+    const value = {
+      primaryPhoneNumber: "'123456'",
+      primaryPhoneCountryCode: "'FR'",
+      primaryPhoneCallingCode: "'33'",
+      additionalPhones: null,
+    };
+
+    expect(phonesFieldDefaultValueSchema.safeParse(value).success).toBe(true);
+  });
+
+  it('should accept a default value with null primary phone subfields', () => {
+    const value = {
+      primaryPhoneNumber: null,
+      primaryPhoneCountryCode: "'FR'",
+      primaryPhoneCallingCode: "'33'",
+      additionalPhones: null,
+    };
+
+    expect(phonesFieldDefaultValueSchema.safeParse(value).success).toBe(true);
+    expect(phonesFieldValueSchema.safeParse(value).success).toBe(false);
+  });
+});

packages/twenty-front/src/modules/object-record/record-field/ui/validation-schemas/phonesFieldDefaultValueSchema.ts

@@ -0,0 +1,16 @@
+import { z } from 'zod';
+
+export const phonesFieldDefaultValueSchema = z.object({
+  primaryPhoneNumber: z.string().nullable(),
+  primaryPhoneCountryCode: z.string().nullable(),
+  primaryPhoneCallingCode: z.string().nullable().optional(),
+  additionalPhones: z
+    .array(
+      z.object({
+        number: z.string(),
+        callingCode: z.string(),
+        countryCode: z.string(),
+      }),
+    )
+    .nullable(),
+});

packages/twenty-front/src/modules/settings/data-model/fields/forms/phones/components/SettingsDataModelFieldPhonesForm.tsx

@@ -1,7 +1,7 @@
 import { Controller, useFormContext } from 'react-hook-form';
 
 import { useFieldMetadataItemById } from '@/object-metadata/hooks/useFieldMetadataItemById';
-import { phonesFieldValueSchema } from '@/object-record/record-field/ui/validation-schemas/phonesFieldValueSchema';
+import { phonesFieldDefaultValueSchema } from '@/object-record/record-field/ui/validation-schemas/phonesFieldDefaultValueSchema';
 import { SettingsOptionCardContentSelect } from '@/settings/components/SettingsOptions/SettingsOptionCardContentSelect';
 import { mergeSettingsSchemas } from '@/settings/data-model/fields/forms/utils/mergeSettingsSchema';
 import { settingsDataModelFieldMaxValuesSchema } from '@/settings/data-model/fields/forms/utils/settingsDataModelFieldMaxValuesSchema';
@@ -28,7 +28,7 @@ type SettingsDataModelFieldPhonesFormProps = {
 
 export const settingsDataModelFieldPhonesFormSchema = z
   .object({
-    defaultValue: phonesFieldValueSchema,
+    defaultValue: phonesFieldDefaultValueSchema,
   })
   .merge(
     mergeSettingsSchemas(
@@ -91,7 +91,7 @@ export const SettingsDataModelFieldPhonesForm = ({
             <Select<string>
               dropdownId="selectDefaultCountryCode"
               value={stripSimpleQuotesFromString(
-                value?.primaryPhoneCountryCode,
+                value?.primaryPhoneCountryCode ?? '',
               )}
               onChange={(newPhoneCountryCode) =>
                 onChange({