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/docker/mount-data.nix

@@ -2,8 +2,8 @@
 
 {
   fileSystems = {
-    "/mnt/docker/config" = {
-      device = "${vars.nfsServerHost}:${vars.storageRoot}/docker/config";
+    ${vars.nfsShares.dockerConfig.mountpoint} = {
+      device = "${vars.nfsServerHost}:${vars.storageRoot}/${vars.nfsShares.dockerConfig.subpath}";
       fsType = "nfs";
 
       options = [
@@ -14,8 +14,8 @@
       ];
     };
 
-    "/mnt/docker/databases" = {
-      device = "${vars.nfsServerHost}:${vars.storageRoot}/docker/databases";
+    ${vars.nfsShares.dockerDatabases.mountpoint} = {
+      device = "${vars.nfsServerHost}:${vars.storageRoot}/${vars.nfsShares.dockerDatabases.subpath}";
       fsType = "nfs";
 
       options = [
@@ -26,8 +26,8 @@
       ];
     };
 
-    "/mnt/docker/volumes" = {
-      device = "${vars.nfsServerHost}:${vars.storageRoot}/docker/volumes";
+    ${vars.nfsShares.dockerVolumes.mountpoint} = {
+      device = "${vars.nfsServerHost}:${vars.storageRoot}/${vars.nfsShares.dockerVolumes.subpath}";
       fsType = "nfs";
 
       options = [
@@ -38,8 +38,8 @@
       ];
     };
 
-    "/mnt/nextcloud-data" = {
-      device = "${vars.nfsServerHost}:${vars.storageRoot}/docker/nextcloud-data";
+    ${vars.nfsShares.nextcloudData.mountpoint} = {
+      device = "${vars.nfsServerHost}:${vars.storageRoot}/${vars.nfsShares.nextcloudData.subpath}";
       fsType = "nfs";
 
       options = [
@@ -50,8 +50,8 @@
       ];
     };
 
-    "/mnt/raspi-backup" = {
-      device = "${vars.nfsServerHost}:${vars.storageRoot}/raspi/volumes";
+    ${vars.nfsShares.raspiVolumes.mountpoint} = {
+      device = "${vars.nfsServerHost}:${vars.storageRoot}/${vars.nfsShares.raspiVolumes.subpath}";
       fsType = "nfs";
 
       options = [