**Enable Nix experimental features system-wide and refactor Nix bootstrap config**

* Rename `config.sh` to `bootstrap_config.sh` to clearly separate installer bootstrap config from Nix system config
* Add `nix_conf_file.sh` to manage `/etc/nix/nix.conf` safely and idempotently
* Ensure `nix-command` and `flakes` are enabled without overwriting existing experimental features
* Invoke Nix config enforcement from `nix/init.sh` during root installation
* Update documentation and ShellCheck annotations accordingly
* Extend CLI git proxy to include `git status`

https://chatgpt.com/share/693d5c4a-bad0-800f-adaf-4719dd4ca377

scripts/nix/lib/nix_conf_file.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Prevent double-sourcing
+if [[ -n "${PKGMGR_NIX_CONF_FILE_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_CONF_FILE_SH=1
+
+nixconf_file_path() {
+  echo "/etc/nix/nix.conf"
+}
+
+nixconf_ensure_experimental_features() {
+  local nix_conf want
+  nix_conf="$(nixconf_file_path)"
+  want="experimental-features = nix-command flakes"
+
+  mkdir -p /etc/nix
+
+  if [[ ! -f "${nix_conf}" ]]; then
+    echo "[nix-conf] Creating ${nix_conf} with: ${want}"
+    printf "%s\n" "${want}" >"${nix_conf}"
+    return 0
+  fi
+
+  if grep -qE '^\s*experimental-features\s*=' "${nix_conf}"; then
+    if grep -qE '^\s*experimental-features\s*=.*\bnix-command\b' "${nix_conf}" \
+      && grep -qE '^\s*experimental-features\s*=.*\bflakes\b' "${nix_conf}"; then
+      echo "[nix-conf] experimental-features already correct"
+      return 0
+    fi
+
+    echo "[nix-conf] Extending experimental-features in ${nix_conf}"
+
+    local current
+    current="$(grep -E '^\s*experimental-features\s*=' "${nix_conf}" | head -n1 | cut -d= -f2-)"
+    current="$(echo "${current}" | xargs)" # trim
+
+    # Build a merged feature string without duplicates (simple token set)
+    local merged="nix-command flakes"
+    local token
+    for token in ${current}; do
+      if [[ " ${merged} " != *" ${token} "* ]]; then
+        merged="${merged} ${token}"
+      fi
+    done
+
+    sed -i "s|^\s*experimental-features\s*=.*|experimental-features = ${merged}|" "${nix_conf}"
+    return 0
+  fi
+
+  echo "[nix-conf] Appending to ${nix_conf}: ${want}"
+  printf "\n%s\n" "${want}" >>"${nix_conf}"
+}