fix(ui): prevent long usernames from overflowing Edit User modal, User Preview modal, and sidebar (#25185)

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

src/lib/components/admin/Users/UserList.svelte

@@ -400,7 +400,7 @@
 								{/if}
 							</div>
 						</td>
-						<td class=" px-3 py-1"> {user.email} </td>
+						<td class=" px-3 py-1 max-w-48 truncate"> {user.email} </td>
 
 						<td class=" px-3 py-1">
 							{dayjs(user.last_active_at * 1000).fromNow()}

src/lib/components/admin/Users/UserList/EditUserModal.svelte

@@ -99,7 +99,7 @@
 								/>
 							</div>
 
-							<div class=" flex-1">
+							<div class=" flex-1 min-w-0">
 								<div class="overflow-hidden w-ful mb-2">
 									<div class=" self-center capitalize font-medium truncate">
 										{selectedUser.name}