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>

common/netconsole-receiver.nix

@@ -0,0 +1,32 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  options.services.netconsoleReceiver = {
+    enable = lib.mkEnableOption "netconsole UDP receiver";
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 6666;
+      description = "UDP port to listen on for netconsole messages";
+    };
+  };
+
+  config = lib.mkIf config.services.netconsoleReceiver.enable {
+    systemd.services.netconsole-receiver = {
+      description = "Netconsole UDP receiver";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      serviceConfig = {
+        ExecStart = "${pkgs.socat}/bin/socat -u UDP-LISTEN:${toString config.services.netconsoleReceiver.port},fork STDOUT";
+        StandardOutput = "journal";
+        StandardError = "journal";
+        SyslogIdentifier = "netconsole";
+        Restart = "always";
+        RestartSec = "5s";
+      };
+    };
+  };
+}