Build Proxmox images directly on the node instead of transferring them

create-proxmox-resource.sh no longer builds locally and scp's a
multi-gigabyte image over -- it now clones/pulls this repo onto the
Proxmox node itself (bootstrapping build tooling via the existing
codex-setup.sh on first use) and runs the nix build / disko image
script there, staging the result straight into the node's own import
directory. host-keys/ (gitignored) is copied over separately since a
git pull doesn't carry it. --image still uploads an explicit local
file for the case where you don't want a build at all.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -114,9 +114,10 @@ Three different paths depending on target, none of them involving a manual
   `docs/proxmox-images.md`.
 
 `scripts/create-proxmox-resource.sh --type lxc|vm --host <name>` automates
-either of the last two end to end (build, host-key registration, upload,
-`pct create`/`qm create`), with `--dry-run` and a guard against duplicating
-an already-deployed host's identity. See its `--help`.
+either of the last two end to end (host-key registration, building the
+image directly on the Proxmox node itself, `pct create`/`qm create`), with
+`--dry-run` and a guard against duplicating an already-deployed host's
+identity. See its `--help`.
 
 ## Security Notes