Long usernames overflow the Edit User modal, User Preview modal header,
and the sidebar user area because the flex containers lack width
constraints.
- EditUserModal: add min-w-0 to the flex-1 container so the existing
truncate class takes effect
- UserPreviewModal: add min-w-0 and truncate to the title container,
flex-shrink-0 to the close button so it stays visible
- Sidebar: add truncate to the username display and flex-shrink-0 to
the avatar container to prevent it from being squeezed
Timothy Jaeryang Baek