Add sync-host-keys.sh and create-proxmox-resource.sh

sync-host-keys.sh: generates/registers SSH host keys and their
.sops.yaml/secrets/*.yaml recipients for flake targets, idempotently.
--all, <target>, --remove, --regenerate-all-keys, all with --dry-run
(verified zero-side-effect via a sandboxed git-status check across every
mode). Only ever touches anchors with a corresponding host-keys/ file --
&admin and any hand-registered real-host anchor are never listed,
removed, or regenerated. Supersedes running prepare-host-key.sh one host
at a time for any target that already has a flake entry.

create-proxmox-resource.sh: builds a lxc-*/proxmox-* target's
tarball/disk image and creates it on a real Proxmox node, or reconfigures
an existing resource's cores/memory/disk (--modify, always requires
typing the VMID back to confirm). Refuses to create a new resource for a
VMID that already exists, and refuses to duplicate a host identity that
already has a real deployment elsewhere (variables.nix's new
deployedTargets, checked by hostName so it also catches cross-platform
duplicates) unless --allow-duplicate-host is passed. --dry-run throughout.

scripts/env.sh centralizes the Proxmox connection config both scripts
(and future ones) share. Also fixes an unrelated gap found along the way:
proxmox-* Disko image builds write their .raw file straight into the
repo root, and .gitignore never covered it.

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

variables.nix

@@ -146,4 +146,21 @@
     maxSize = "100M"; # rotate once a log file exceeds this size
     keep = 20; # number of rotated logs to retain before deleting the oldest
   };
+
+  # Flake targets with a real, currently-running deployment somewhere —
+  # matches README.md's Hosts table "(real, deployed)" annotations; update
+  # both together. Not consumed by any NixOS module (nothing in the actual
+  # system config should behave differently because of this) — it's read
+  # by scripts/create-proxmox-resource.sh to refuse creating a same-identity
+  # duplicate of an already-deployed host (shared hostName/hostId) unless
+  # you explicitly pass --allow-duplicate-host.
+  deployedTargets = [
+    "linode-minimal"
+    "proxmox-minimal"
+    "proxmox-nix-cache"
+    "proxmox-server"
+    "proxmox-docker"
+    "proxmox-gui"
+    "proxmox-pxe-boot"
+  ];
 }