feat: Add server failure simulation to load balancer (#795)

* feat: Add server failure simulation to load balancer (fixes #794)

- Click servers to toggle healthy/offline state
- Minimal UI: compact controls, smaller diagram (h-48 vs h-72)
- Inline stats row instead of large cards
- Failed requests shown only when > 0
- All algorithms handle failures appropriately

* feat: Add server failure simulation to load balancer (fixes #794)

- Click on server icons to toggle healthy/offline state
- Offline servers shown with X icon and gray color
- Requests to offline servers fail and bounce back (red dot)
- Failed request counter in header
- All algorithms handle server failures appropriately
- Visual hint in description to indicate servers are clickable

* fix: Adjust layout to fit all servers in visualization window

- Increase container height from h-72 to h-80 (320px)
- Reduce server padding from py-6 to py-4
- Adjust Y positions from [20,50,80] to [18,50,82]
- Compact server labels (text-xs, mt-1)

Author: bobbyonmagic