Consolidate CI on codex-maintenance.sh; clean up dead scripts and docs

Both check-nixos.yml workflows (GitHub + Gitea) now call
scripts/codex-maintenance.sh instead of a hand-rolled eval-only loop,
closing a real gap: CI previously enforced none of the secret grep,
nixpkgs-fmt, or statix checks that codex-maintenance.sh already runs
locally — nothing was stopping that from regressing. One script now
backs both, instead of two copies that can drift from each other.

codex-maintenance.sh itself is extended to cover buildable surface
that wasn't validated anywhere before: packages.x86_64-linux.*, plus
config.system.build.tarball (lxc-* hosts) and
config.system.build.diskoImagesScript (proxmox-*, excluding the
installer's own proxmox-lxc target, which has no disko config).

Also:
- scripts/prepare-host-key.sh: dropped the redundant
  [path-to-nixos-repo] parameter — it always defaults to the repo the
  script itself lives in now, so a second argument never made sense
  after the nix-auto-installer migration.
- Removed prepare.sh (dead pre-disko manual parted/mkfs/mkswap
  partitioning, fully superseded) and
  scripts/create-linode-installer-disk.sh (incomplete draft for an
  abandoned dd-via-rescue-mode approach; Linode hosts already deploy
  fine through the normal auto-installer flow).
- docs/pxe-boot.md: fixed a stale `nixosConfigurations.pxe-boot` eval
  command (pre-refactor flat name, not a real flake attribute
  anymore) and added a cross-reference to docs/auto-installer.md.
- CLAUDE.md/README.md: full documentation pass reconciling this
  session's changes — modules/installer/, modules/pxe-boot/, the
  LXC/Proxmox image-building deployment paths, corrected the
  password-hash/SSH-key locations in the safety-rules section (both
  had drifted to reference files/paths that no longer exist), and
  added session-workflow guidance to prefer targeted host evals over
  full-repo sweeps for incremental changes (explicitly scoped to
  interactive sessions, not CI).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01La55Nsss8jZ7ZuzUV9mfot

README.md

@@ -55,7 +55,7 @@ nix eval --json .#nixosConfigurations --apply builtins.attrNames | jq -r '.[]'
 | `modules/nix-cache/` | Binary cache and remote builder client/server modules |
 | `modules/installer/` | Auto-installer environment (ISO/netboot/Proxmox LXC) — see `docs/auto-installer.md` |
 | `host-keys/` | Gitignored, locally-generated SSH host keys for the auto-installer — see `docs/auto-installer.md` |
-| `docs/` | Operational notes for cache, builders, lock updates, boot services, and the auto-installer |
+| `docs/` | Operational notes for cache, builders, lock updates, boot services, the auto-installer, and Proxmox image builds |
 | `scripts/` | Codex setup, validation, and host-key-prep helpers |
 
 ## Validation
@@ -87,6 +87,20 @@ review sessions.
   client hosts.
 - `pxe-boot` serves iPXE boot files over HTTP from `/srv/pxe`.
 
+### Deploying a new host
+
+Three different paths depending on target, none of them involving a manual
+`nixos-rebuild switch` from this repo:
+
+- Most hosts: boot the auto-installer, pick the target from its menu — see
+  `docs/auto-installer.md`.
+- `lxc-*` targets: not installed at all — build a ready-to-run container
+  tarball and `pct restore` it directly. `docs/auto-installer.md` covers why
+  (and the installer's menu excludes them for the same reason).
+- `proxmox-*` targets: can alternatively be built as a standalone `.raw`
+  disk image and attached to a new VM with no install step — see
+  `docs/proxmox-images.md`.
+
 ## Security Notes
 
 Do not commit tokens, private keys, live credentials, or new password hashes
@@ -107,6 +121,13 @@ enabled via `git config core.hooksPath .githooks`, done automatically by
 `scripts/codex-setup.sh`) runs `gitleaks protect --staged` to catch mistakes
 before they're committed.
 
+The auto-installer environment is the one deliberate exception to
+sops-nix-everywhere: it has a hardcoded login password instead (no stable
+per-boot host key for sops-nix to derive from on ephemeral media) — see
+"Host keys" in `docs/auto-installer.md` for why, and how the private keys it
+*does* pre-seed for target hosts stay out of git via the gitignored
+`host-keys/` directory.
+
 This repository's git *history* still contains secrets committed before this
 migration (see `remove-sensetive-info-refactor.md`) — those are being
 scrubbed and rotated separately; don't treat the repo as safe to make public