Make lxc-docker a privileged container: unprivileged can't NFS-mount at all

The kernel's NFS client filesystem doesn't set FS_USERNS_MOUNT, so mounting
NFS from inside any non-init user namespace -- exactly what an unprivileged
LXC container's UID-mapped root runs in -- is rejected at the VFS layer
with EPERM, regardless of Proxmox's mount=nfs;nfs4 container feature (which
only patches the AppArmor layer). Confirmed live on the redeployed lxc-docker
container: TCP to the NFS server's port 2049 succeeds, the server's export
table matches the container's IP, and mount.nfs: Operation not permitted
still fires immediately with no corresponding denial anywhere in the
server's own logs -- a kernel-level rejection that no amount of DNS/
automount/export tweaking (this branch's earlier commits) could ever fix.

modules/platforms/lxc.nix now keys proxmoxLXC.privileged off hostName
("docker" -> true) rather than a blanket false, since build-types/docker.nix
is also composed for linode-docker/proxmox-docker, which don't import
proxmox-lxc.nix at all -- setting this option there would break their eval.
create-proxmox-resource.sh reads the value back via a new
flake_target_lxc_privileged helper instead of hardcoding --unprivileged 1,
so the two stay in sync automatically for every lxc-* target.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T48qgH3VTvs8wvwj44FEbE

scripts/lib/nix-eval.sh

@@ -34,3 +34,21 @@ flake_target_hostname() {
   nix eval --raw "${NIX_EVAL_FLAGS[@]}" \
     "${flake_ref}#nixosConfigurations.${target}.config.networking.hostName" 2>/dev/null
 }
+
+# flake_target_lxc_privileged <flake_ref> <target>
+# Prints "true" or "false" for one lxc-* target's config.proxmoxLXC.privileged
+# (modules/platforms/lxc.nix is the single source of truth -- e.g.
+# lxc-docker sets this true so it can NFS-mount; every other lxc-* host
+# stays unprivileged). Only meaningful for lxc-* targets -- the option
+# doesn't exist for linode-*/proxmox-* (nixpkgs' proxmox-lxc.nix, which
+# declares it, is only ever imported by modules/platforms/lxc.nix). Empty
+# (not an error under set -e) if the eval fails.
+flake_target_lxc_privileged() {
+  local flake_ref="$1" target="$2"
+  # Not --raw: the option is a Nix boolean, and --raw can only coerce
+  # strings ("cannot coerce a Boolean to a string"). Plain `nix eval`
+  # prints a bare `true`/`false` for a boolean, which is exactly the
+  # string this needs.
+  nix eval "${NIX_EVAL_FLAGS[@]}" \
+    "${flake_ref}#nixosConfigurations.${target}.config.proxmoxLXC.privileged" 2>/dev/null
+}