Replace the duplicate-host check with a live Proxmox query, drop deployedTargets

variables.nix's deployedTargets was a manually-maintained list with no
enforcement keeping it in sync with reality -- it caused two separate
false refusals in a row (naming a VM as deployed well after it had been
destroyed, then matching a target against itself once the list was
"corrected"). Static files can't track whether a resource still actually
exists.

create-proxmox-resource.sh's duplicate-host guard now queries the
Proxmox node directly (qm/pct's own name/hostname config, matched
against --host) instead. Also fixes a gap in that live check: it
originally swallowed ssh failures and would have silently treated "can't
reach the node" the same as "checked, nothing there" -- it now refuses
instead of guessing when the node can't be reached.

deployedTargets is removed entirely from variables.nix since nothing
else in the repo consumed it once this script no longer does; README.md's
Hosts table remains the sole source of truth for "(real, deployed)"
status. CLAUDE.md and the script's own --help/comments updated to match.

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

variables.nix

@@ -156,20 +156,4 @@
     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"
-    "lxc-nix-cache"
-    "proxmox-server"
-    "proxmox-docker"
-    "proxmox-gui"
-    "proxmox-pxe-boot"
-  ];
 }