Expand variables.nix: NFS shares, ports, image size, GC/rotation, Pi host

Adds nested vars.nfsShares (subpath + mountpoint per dataset, previously
duplicated independently across server.nix's NFS exports, mount-data.nix's
client mounts, docker.nix's tmpfiles rules, traefik's log rotation path,
and hosts/server/host.nix's beszel config), vars.ports (every literal port
in modules/ and hosts/, kept as separate entries per service even where
numbers coincide so changing one can't silently change another), plus
vars.proxmoxImageSize, vars.nixCacheGcMaxAge, vars.traefikLogRotate, and
raspberryPiHost/raspiNfsPath/raspiMountpoint for the Pi's own NFS export.

Also fixes docker.nix/minimal.nix/gui.nix hardcoding the literal "nixos"
username instead of the existing vars.primaryUser, found during the sweep.

system.stateVersion is deliberately left untouched everywhere -- per
NixOS's own docs that value must stay fixed from first install, not
follow any shared variable.

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

modules/build-types/docker.nix

@@ -28,13 +28,18 @@
   boot.supportedFilesystems = [ "nfs" ];
 
   systemd.tmpfiles.rules = [
-    "L+ /home/nixos/docker - - - - /mnt/docker/config"
-    "d /mnt/docker 0755 nixos users -"
-    "d /mnt/raspi-backup 0755 nixos users -"
+    "L+ /home/${vars.primaryUser}/docker - - - - ${vars.nfsShares.dockerConfig.mountpoint}"
+    "d /mnt/docker 0755 ${vars.primaryUser} users -"
+    "d ${vars.nfsShares.raspiVolumes.mountpoint} 0755 ${vars.primaryUser} users -"
   ];
 
-  users.users.nixos.extraGroups = [ "docker" ];
+  users.users.${vars.primaryUser}.extraGroups = [ "docker" ];
   services.openssh.settings.PermitRootLogin = "yes";
 
-  networking.firewall.allowedTCPPorts = [ 80 8080 443 vars.beszelHubPort ];
+  networking.firewall.allowedTCPPorts = [
+    vars.ports.dockerHttp
+    vars.ports.dockerExtra
+    vars.ports.dockerHttps
+    vars.ports.beszelHub
+  ];
 }