fix: default PROXMOX_REMOTE_REPO_DIR to SSH user's home dir

/root/nixos was only correct when PROXMOX_SSH_USER=root. Now that it
defaults to wayne, use /home/${PROXMOX_SSH_USER}/nixos so git clone
goes somewhere the SSH user can actually write to.

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

scripts/env.sh

@@ -30,7 +30,7 @@
 # (from this checkout's own `origin` remote) the first time it doesn't
 # find it, installing build tooling via scripts/codex-setup.sh, then
 # `git pull`s it before every subsequent build.
-: "${PROXMOX_REMOTE_REPO_DIR:=/root/nixos}"
+: "${PROXMOX_REMOTE_REPO_DIR:=/home/${PROXMOX_SSH_USER}/nixos}"
 
 # Storage pool names -- Proxmox's own stock-install defaults, but this
 # varies a lot by setup (ZFS pool name, custom LVM-thin volume, etc.).