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

modules/platforms/lxc.nix

@@ -1,4 +1,4 @@
-{ lib, modulesPath, flakeTarget, ... }:
+{ config, lib, modulesPath, flakeTarget, ... }:
 
 let
   # Bakes this exact flake target's pre-generated SSH host key straight
@@ -58,8 +58,28 @@ in
     # host.nix declares each host's real hostname (networking.hostName);
     # keep that instead of letting Proxmox's ambient container config win.
     manageHostName = true;
-    # Unprivileged matches how these containers are actually created.
-    privileged = false;
+    # Unprivileged by default -- matches how these containers are actually
+    # created (scripts/proxmox/create-proxmox-resource.sh reads this value
+    # back to decide `pct create`'s --unprivileged flag, so the two stay
+    # in sync).
+    #
+    # lxc-docker is the one exception: the kernel's NFS client doesn't set
+    # FS_USERNS_MOUNT, so mounting NFS from inside *any* non-init user
+    # namespace -- which is exactly what an unprivileged container's
+    # UID-mapped root runs in -- is rejected at the VFS layer with EPERM,
+    # no matter what Proxmox's own `mount=nfs;nfs4` container feature
+    # allows at the AppArmor layer (confirmed live: TCP to the NFS server
+    # 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 logs -- a kernel-level
+    # rejection, not a network or export-permission one). Keying off
+    # hostName rather than something docker-build-type-specific because
+    # modules/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 with "option does not
+    # exist" regardless of any mkIf guard, since mkIf only makes a value
+    # conditional, not whether the option needs to exist somewhere.
+    privileged = config.networking.hostName == "docker";
   };
 
   boot.loader = {