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  partitioning, fully superseded) and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

scripts/codex-maintenance.sh

@@ -55,6 +55,33 @@ echo "Evaluating host toplevel derivations..."
 for host in $hosts; do
   echo "==> $host"
   nix eval --raw --no-use-registries --no-accept-flake-config ".#nixosConfigurations.${host}.config.system.build.toplevel.drvPath"
+
+  # lxc-* hosts deploy via a directly pct-restore-able tarball instead of
+  # nixos-install (see docs/auto-installer.md); proxmox-* hosts (excluding
+  # proxmox-lxc, the installer's own LXC target, which has no disko config)
+  # can alternatively be built as a standalone disk image (see
+  # docs/proxmox-images.md). Both are otherwise-unvalidated buildable
+  # surface, easy to silently break without this.
+  case "$host" in
+    lxc-*)
+      echo "==> $host (tarball)"
+      nix eval --raw --no-use-registries --no-accept-flake-config ".#nixosConfigurations.${host}.config.system.build.tarball.drvPath"
+      ;;
+    proxmox-lxc) ;;
+    proxmox-*)
+      echo "==> $host (diskoImagesScript)"
+      nix eval --raw --no-use-registries --no-accept-flake-config ".#nixosConfigurations.${host}.config.system.build.diskoImagesScript.drvPath"
+      ;;
+  esac
+done
+
+echo
+echo "Evaluating buildable packages..."
+packages_json="$(nix eval --json --no-use-registries --no-accept-flake-config .#packages.x86_64-linux --apply builtins.attrNames)"
+packages="$(echo "$packages_json" | jq -r '.[]')"
+for pkg in $packages; do
+  echo "==> packages.x86_64-linux.${pkg}"
+  nix eval --raw --no-use-registries --no-accept-flake-config ".#packages.x86_64-linux.${pkg}"
 done
 
 if [[ "$MODE" == "dry-run" ]]; then
@@ -63,6 +90,25 @@ if [[ "$MODE" == "dry-run" ]]; then
   for host in $hosts; do
     echo "==> Dry-run build: $host"
     nix build --dry-run --no-link --no-use-registries --no-accept-flake-config ".#nixosConfigurations.${host}.config.system.build.toplevel"
+
+    case "$host" in
+      lxc-*)
+        echo "==> Dry-run build: $host (tarball)"
+        nix build --dry-run --no-link --no-use-registries --no-accept-flake-config ".#nixosConfigurations.${host}.config.system.build.tarball"
+        ;;
+      proxmox-lxc) ;;
+      proxmox-*)
+        echo "==> Dry-run build: $host (diskoImagesScript)"
+        nix build --dry-run --no-link --no-use-registries --no-accept-flake-config ".#nixosConfigurations.${host}.config.system.build.diskoImagesScript"
+        ;;
+    esac
+  done
+
+  echo
+  echo "Running dry-run builds for all packages."
+  for pkg in $packages; do
+    echo "==> Dry-run build: packages.x86_64-linux.${pkg}"
+    nix build --dry-run --no-link --no-use-registries --no-accept-flake-config ".#packages.x86_64-linux.${pkg}"
   done
 fi