feat(shell): make Switch-nix/Test-nix/buildImage system-wide

IPA users (e.g. wayne@) don't get Home Manager so the aliases defined in
aliases.nix were invisible to them. Move Switch-nix, Test-nix, and
buildImage into programs.bash in configuration.nix so every user on every
host gets them via /etc/bashrc. Stub out aliases.nix for future per-user
HM-only additions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/common/configuration.nix

@@ -1,5 +1,29 @@
 { config, lib, pkgs, vars, ... }:
 
+let
+  switchCmd = ''
+    sudo nixos-rebuild switch \
+      --no-write-lock-file \
+      --refresh \
+      --flake git+https://${vars.lanDomain}/beatzaplenty/nixos.git#$(cat /etc/flake-target)
+  '';
+  testCmd = ''
+    sudo nixos-rebuild test \
+      --no-write-lock-file \
+      --refresh \
+      --flake git+https://${vars.lanDomain}/beatzaplenty/nixos.git#$(cat /etc/flake-target)
+  '';
+  buildImageFn = ''
+    buildImage() {
+      if [ -z "$1" ]; then
+        echo "usage: buildImage <flake-target>  (e.g. lxc-docker)" >&2
+        return 1
+      fi
+      NIXOS_HOST_KEYS_DIR="$(pwd)/host-keys" nix build --impure \
+        ".#nixosConfigurations.$1.config.system.build.tarball"
+    }
+  '';
+in
 {
   imports =
     [
@@ -8,6 +32,16 @@
       ./set-locale.nix
       ../ipa/client.nix
     ];
+
+  # System-wide shell config so all users (including IPA accounts) get the
+  # same management aliases as the local nixos user's Home Manager provides.
+  programs.bash = {
+    shellAliases = {
+      "Switch-nix" = switchCmd;
+      "Test-nix" = testCmd;
+    };
+    interactiveShellInit = buildImageFn;
+  };
   # Use the GRUB 2 boot loader.
   # boot.loader.grub.enable = true;
   #boot.loader.grub.device = "/dev/sda"; # or "nodev" for efi only