chore: drop omarchy pkg-* compatibility shims

These existed only to ease muscle-memory from Arch-based distros and add
no behavior on a Nix-native system:

- nomarchy-pkg-install — alias for nomarchy-pkg-add
- nomarchy-pkg-drop    — alias for nomarchy-pkg-remove
- nomarchy-pkg-aur-add — stub that only printed "AUR doesn't exist on NixOS"

The single code caller (nomarchy-voxtype-remove) was removed in the prior
commit, so the shims have no remaining references. SKILL.md updated to use
nomarchy-pkg-add and to point at `nix search nixpkgs` instead of the AUR.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

features/scripts/utils/nomarchy-pkg-aur-add

@@ -1,9 +0,0 @@
-#!/usr/bin/env bash
-set -e
-
-# Nomarchy AUR Stub
-# Informs the user that AUR is not applicable to NixOS.
-
-notify-send -u critical "Nomarchy" "The AUR is an Arch Linux feature and is not available on NixOS. Try searching for the package in nixpkgs using 'nix search nixpkgs <name>'."
-echo "Error: AUR is not available on NixOS."
-exit 1

features/scripts/utils/nomarchy-pkg-drop

@@ -1,7 +0,0 @@
-#!/usr/bin/env bash
-set -e
-
-# Nomarchy Package Drop Script
-# Alias for nomarchy-pkg-remove.
-
-nomarchy-pkg-remove "$@"

features/scripts/utils/nomarchy-pkg-install

@@ -1,7 +0,0 @@
-#!/usr/bin/env bash
-set -e
-
-# Nomarchy Package Install Script
-# Alias for nomarchy-pkg-add for users coming from other distros.
-
-nomarchy-pkg-add "$@"