fix: width in PageHeader comp (#7866)

Fixes: #7864 


This fix prevents layout issues caused by invalid CSS and ensures that
the PageHeader component works correctly when no width prop is passed.

![Screenshot from 2024-10-20
00-03-39](https://github.com/user-attachments/assets/68340256-c756-4a56-9028-9aed32caf68e)

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-front/src/modules/ui/layout/page/components/PageHeader.tsx

@@ -31,7 +31,7 @@ const StyledTopBarContainer = styled.div<{ width?: number }>`
   padding: ${({ theme }) => theme.spacing(2)};
   padding-left: 0;
   padding-right: ${({ theme }) => theme.spacing(3)};
-  width: ${({ width }) => width + 'px' || '100%'};
+  width: ${({ width }) => (width ? `${width}px` : '100%')};
 
   @media (max-width: ${MOBILE_VIEWPORT}px) {
     width: 100%;