add homelab rebuild just recipes

Justfile

@@ -0,0 +1,25 @@
+nixos_rebuild := "github:NixOS/nixpkgs/nixos-25.11#nixos-rebuild"
+
+# List available homelab commands.
+default:
+    @just --list
+
+# Activate a host configuration without making it the boot default.
+[group('homelab')]
+test host:
+    @just _rebuild {{ host }} test
+
+# Activate a host configuration and make it the boot default.
+[group('homelab')]
+switch host:
+    @just _rebuild {{ host }} switch
+
+_rebuild host action:
+    @case "{{ host }}" in yggdrasil|midgard) ;; *) echo "unknown host: {{ host }}" >&2; exit 2;; esac
+    nix run {{ nixos_rebuild }} -- \
+      {{ action }} \
+      --fast \
+      --flake ".#{{ host }}" \
+      --build-host "{{ host }}" \
+      --target-host "{{ host }}" \
+      --use-remote-sudo