feat(nfs): centralize nixdesk jellyfin nfs client module

Move the nixdesk jellyfin NFS client configuration from individual
host services to a centralized NixOS module in `modules/system/nfs/`.

This change:
- Creates `modules/system/nfs/default.nix` containing the `nixdeskJellyfin`
  flake module.
- Removes redundant NFS client definitions from `modules/hosts/nix-server/`
  and `modules/hosts/r5500/`.
- Updates `modules/hosts/r5500/configuration.nix` to use the new
  centralized module.
- Cleans up unused local disk configuration in `modules/hosts/14900k/`.

modules/hosts/r5500/_services/nixdesk-nfs-client.nix

@@ -1,28 +0,0 @@
-# NFS mounts of nixdesk (14900k) bulk storage for r5500. Exports live in
-#   modules/hosts/14900k/_private/jellyfin-nfs-export.nix
-#
-# Jellyfin library paths:
-#   Movies → /mnt/nixdesk-jellyfin/movies
-#   Shows  → /mnt/nixdesk-jellyfin/tv
-{ ... }:
-let
-  nfsExportHost = "192.168.2.25";
-  nfsClientOpts = [
-    "rw"
-    "noatime"
-    "nofail"
-    "_netdev"
-    "nfsvers=3"
-    "tcp"
-    "lookupcache=none"
-    "x-systemd.automount"
-    "x-systemd.idle-timeout=3600"
-  ];
-in
-{
-  fileSystems."/mnt/nixdesk-jellyfin" = {
-    device = "${nfsExportHost}:/mnt/deep/jellyfin";
-    fsType = "nfs";
-    options = nfsClientOpts;
-  };
-}

modules/hosts/r5500/configuration.nix

@@ -17,7 +17,7 @@
         ./_private/media-disk.nix
         ./_private/media-paths.nix
         ./_services/docker-media.nix
-        ./_services/nixdesk-nfs-client.nix
+        self.nixosModules.nixdeskJellyfin
         ./_services/jellyfin.nix
         ./_services/sonarr.nix
         ./_services/radarr.nix