fix(localization): parse date-only ISO strings as local midnight in relative date formatter (#20630)

## Summary

Fixes #19634

### Root Cause

The ECMAScript spec treats date-only strings (`YYYY-MM-DD`) as **UTC
midnight** when passed to `new Date()`. But `date-fns` comparison
functions (`isToday`, `isYesterday`, `isTomorrow`) operate in **local
time**. For users in UTC-negative timezones, UTC midnight April 14 is
April 13 evening locally — so the label shows "Yesterday" instead of
"Today".

### Fix

In `formatDateISOStringToRelativeDate.ts`, detect date-only strings
(length === 10) and append `T00:00:00` (no `Z`) to force local-time
parsing:

```ts
// Before
const targetDate = new Date(isoDate);

// After
const targetDate =
  isoDate.length === 10 ? new Date(isoDate + 'T00:00:00') : new Date(isoDate);
```

Full datetime strings (with time component) are left unchanged — they
already carry timezone information.

### Tests

Added `formatDateISOStringToRelativeDate.test.ts` covering:
- `Today` / `Yesterday` / `Tomorrow` labels for date-only strings
- Regression case: date-only string parsed at local midnight (not UTC
midnight)
- Full datetime strings continue to work as before

## Before / After

| Scenario | Before | After |
|---|---|---|
| `"2026-04-14"` viewed at UTC-5 on April 14 | Yesterday ❌ | Today ✓ |
| `"2026-04-14"` viewed at UTC+0 on April 14 | Today ✓ | Today ✓ |
| `"2026-04-14T12:00:00Z"` | Today ✓ | Today ✓ |

---------

Co-authored-by: Marie Stoppa <marie@twenty.com>

packages/twenty-front/src/utils/string/__tests__/formatDateString.test.ts

@@ -1,7 +1,7 @@
 import { DateFormat } from '@/localization/constants/DateFormat';
 import { FieldDateDisplayFormat } from '@/object-record/record-field/ui/types/FieldMetadata';
-import { enUS } from 'date-fns/locale';
 import { subDays } from 'date-fns';
+import { enUS } from 'date-fns/locale';
 import { formatDateString } from '~/utils/string/formatDateString';
 
 describe('formatDateString', () => {
@@ -112,4 +112,98 @@ describe('formatDateString', () => {
 
     expect(result).toBe(mockFormattedDate);
   });
+
+  describe('date-only values across user timezones', () => {
+    it('should render the same calendar date for a UTC user', () => {
+      const result = formatDateString({
+        ...defaultParams,
+        value: '2022-01-01',
+        timeZone: 'UTC',
+        localeCatalog: enUS,
+      });
+
+      expect(result).toBe('1 Jan, 2022');
+    });
+
+    it('should render the same calendar date for a negative-offset user', () => {
+      const result = formatDateString({
+        ...defaultParams,
+        value: '2022-01-01',
+        timeZone: 'America/Los_Angeles',
+        localeCatalog: enUS,
+      });
+
+      expect(result).toBe('1 Jan, 2022');
+    });
+
+    it('should render the same calendar date for a positive-offset user', () => {
+      const result = formatDateString({
+        ...defaultParams,
+        value: '2022-01-01',
+        timeZone: 'Asia/Tokyo',
+        localeCatalog: enUS,
+      });
+
+      expect(result).toBe('1 Jan, 2022');
+    });
+
+    it('should render a date-only value with CUSTOM displayFormat without timezone shift', () => {
+      const result = formatDateString({
+        ...defaultParams,
+        value: '2022-01-01',
+        timeZone: 'America/Los_Angeles',
+        dateFieldSettings: {
+          displayFormat: FieldDateDisplayFormat.CUSTOM,
+          customUnicodeDateFormat: 'yyyy-MM-dd',
+        },
+        localeCatalog: enUS,
+      });
+
+      expect(result).toBe('2022-01-01');
+    });
+  });
+
+  describe('date-only values with RELATIVE displayFormat across timezones', () => {
+    beforeAll(() => {
+      jest.useFakeTimers();
+    });
+
+    afterAll(() => {
+      jest.useRealTimers();
+    });
+
+    it('should return "Tomorrow" when the target value is the next calendar day in the user timezone', () => {
+      // 2026-05-18 13:00 UTC: today in UTC is May 18, so "2026-05-19" is tomorrow.
+      jest.setSystemTime(new Date('2026-05-18T13:00:00Z'));
+
+      const result = formatDateString({
+        ...defaultParams,
+        value: '2026-05-19',
+        timeZone: 'UTC',
+        dateFieldSettings: {
+          displayFormat: FieldDateDisplayFormat.RELATIVE,
+        },
+        localeCatalog: enUS,
+      });
+
+      expect(result).toBe('Tomorrow');
+    });
+
+    it('should return "Today" for the same value when the user timezone has already rolled over', () => {
+      // 2026-05-18 21:00 UTC = 2026-05-19 06:00 in Asia/Tokyo, so "2026-05-19" is today there.
+      jest.setSystemTime(new Date('2026-05-18T21:00:00Z'));
+
+      const result = formatDateString({
+        ...defaultParams,
+        value: '2026-05-19',
+        timeZone: 'Asia/Tokyo',
+        dateFieldSettings: {
+          displayFormat: FieldDateDisplayFormat.RELATIVE,
+        },
+        localeCatalog: enUS,
+      });
+
+      expect(result).toBe('Today');
+    });
+  });
 });

packages/twenty-front/src/utils/string/formatDateString.ts

@@ -31,6 +31,7 @@ export const formatDateString = ({
         isoDate: value,
         isDayMaximumPrecision: true,
         localeCatalog,
+        timeZone,
       });
     case FieldDateDisplayFormat.USER_SETTINGS:
       return formatDateISOStringToDate({

packages/twenty-front/src/utils/string/formatDateTimeString.ts

@@ -32,7 +32,8 @@ export const formatDateTimeString = ({
     case FieldDateDisplayFormat.RELATIVE:
       return formatDateISOStringToRelativeDate({
         isoDate: value,
-        localeCatalog: localeCatalog,
+        localeCatalog,
+        timeZone,
       });
     case FieldDateDisplayFormat.USER_SETTINGS:
       return formatDateISOStringToDateTime({