Add stability debugging for beefy lockups.

- Add netconsole receiver on zippy to capture kernel messages
- Configure beefy as netconsole sender to zippy (192.168.1.2)
- Enable kdump with 256M reserved memory for crash analysis
- Add lockup detectors (softlockup_panic, hung_task_panic, nmi_watchdog)
- Add consoleblank=300 for greeter display sleep
- Persist crash dumps and add analysis tools (crash, makedumpfile)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

hosts/zippy/default.nix

@@ -5,9 +5,13 @@
     ../../common/global
     ../../common/cluster-member.nix  # Consul + storage clients
     ../../common/nomad-worker.nix     # Nomad client (runs jobs)
+    ../../common/netconsole-receiver.nix
     ./hardware.nix
   ];
 
+  # Receive kernel messages from beefy via netconsole
+  services.netconsoleReceiver.enable = true;
+
   diskLayout = {
     mainDiskDevice = "/dev/disk/by-id/ata-KINGSTON_SKC600MS1024G_50026B7785AE0A92";
     #keyDiskDevice = "/dev/disk/by-id/usb-Intenso_Micro_Line_22080777660702-0:0";