Consolidate minimal-buildtype hosts onto a single nix-minimal identity

linode-minimal, proxmox-minimal, and lxc-minimal now all share
hosts/nix-minimal/host.nix instead of three separate per-platform
host files with different hostnames — every minimal-buildtype host is
named nix-minimal regardless of which platform it runs on.

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

hosts/linode-minimal/host.nix

@@ -1,9 +0,0 @@
-{ ... }:
-
-{
-  networking.hostName = "linode-minimal";
-
-  # Preserved from the pre-refactor `linode-minimal` target — stateVersion
-  # must never be bumped on an already-installed machine.
-  system.stateVersion = "26.05";
-}

hosts/lxc-minimal/host.nix

@@ -1,9 +0,0 @@
-{ ... }:
-
-{
-  networking.hostName = "lxc-minimal";
-
-  # No pre-existing deployed machine to preserve — pin explicitly to the
-  # current release rather than let it silently default.
-  system.stateVersion = "26.05";
-}