added hm cli utility

packages/hm-cli.nix

@@ -0,0 +1,101 @@
+{
+  pkgs ? import <nixpkgs> { },
+}:
+
+pkgs.writeShellScriptBin "hm" ''
+    set -e
+
+    HM="${pkgs.lib.getExe pkgs.home-manager}"
+    FLAKE_PATH="''${HM_PATH:-$HOME/.config/home-manager}"
+    FLAKE_OUTPUT="''${HM_USER:-$(whoami)@$(hostname)}"
+
+    show_usage() {
+      cat <<EOF
+  Usage: hm <command> [args]
+
+  Commands:
+    apply                       Switch to a new generation
+    generation list             List all generations
+    generation delete ID...     Delete specified generation(s)
+    generation rollback         Rollback to the previous generation
+    generation switch ID        Switch to the specified generation
+    generation cleanup          Delete all but the current generation
+
+  Environment Variables:
+    HM_PATH           Override default flake path (~/.config/home-manager)
+      Currently set to "$(echo $HM_PATH)"
+    HM_USER           Override default user output ("$(whoami)@$(hostname)")
+      Currently set to "$(echo $HM_USER)"
+  EOF
+    }
+
+    if [[ $# -eq 0 ]]; then
+      show_usage
+      exit 1
+    fi
+
+    case "$1" in
+      apply)
+        "$HM" switch --flake "$FLAKE_PATH#$FLAKE_OUTPUT"
+        ;;
+      generation)
+        if [[ $# -lt 2 ]]; then
+          echo "Error: generation command requires a subcommand"
+          show_usage
+          exit 1
+        fi
+
+        case "$2" in
+          list)
+            "$HM" generations
+            ;;
+          delete)
+            if [[ $# -lt 3 ]]; then
+              echo "Error: delete requires at least one generation ID"
+              exit 1
+            fi
+            shift 2
+            "$HM" remove-generations "$@"
+            ;;
+          rollback)
+            "$HM" generations | \
+              sed -n 's/^[[:space:]]*id \([0-9]\+\).*/\1/p' | \
+              head -n 2 | tail -n 1 | \
+              xargs -I {} "$HM" switch --flake "$FLAKE_PATH" --switch-generation {}
+            ;;
+          switch)
+            if [[ $# -ne 3 ]]; then
+              echo "Error: switch requires exactly one generation ID"
+              exit 1
+            fi
+            "$HM" switch --flake "$FLAKE_PATH" --switch-generation "$3"
+            ;;
+          cleanup)
+            CURRENT_GEN=$("$HM" generations | sed -n 's/^[[:space:]]*id \([0-9]\+\) (current).*/\1/p')
+            if [[ -z "$CURRENT_GEN" ]]; then
+              echo "Error: could not determine current generation"
+              exit 1
+            fi
+            OLD_GENS=$("$HM" generations | sed -n 's/^[[:space:]]*id \([0-9]\+\).*/\1/p' | grep -v "^$CURRENT_GEN$")
+            if [[ -z "$OLD_GENS" ]]; then
+              echo "No old generations to delete"
+            else
+              echo "Deleting generations: $(echo $OLD_GENS | tr '\n' ' ')"
+              echo "$OLD_GENS" | xargs "$HM" remove-generations
+              echo "Cleanup complete. Current generation $CURRENT_GEN preserved."
+            fi
+            ;;
+          *)
+            echo "Error: unknown generation subcommand '$2'"
+            show_usage
+            exit 1
+            ;;
+        esac
+        ;;
+      *)
+        echo "Error: unknown command '$1'"
+        show_usage
+        exit 1
+        ;;
+    esac
+''