The Mantine Indicator component (used by the Proxmox cluster health widget for VM/LXC status dots) sits at z-index 200, which is higher than the AppShellHeader's default 100. This caused the status dots to bleed above the header when scrolling. Set the header z-index to 201 so it stacks above Indicator content without conflicting with modal/popover layers (300+). Closes #6194