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-shared/src/utils/index.ts

@@ -29,6 +29,7 @@ export { interpolateCommandMenuItemTemplate } from './command-menu-items/interpo
 export { resolveObjectMetadataLabel } from './command-menu-items/resolveObjectMetadataLabel';
 export { safeGetNestedProperty } from './command-menu-items/safeGetNestedProperty';
 export { computeDiffBetweenObjects } from './compute-diff-between-objects';
+export { isDateWithoutTime } from './date/isDateWithoutTime';
 export { isPlainDateAfter } from './date/isPlainDateAfter';
 export { isPlainDateBefore } from './date/isPlainDateBefore';
 export { isPlainDateBeforeOrEqual } from './date/isPlainDateBeforeOrEqual';