Implement r5500 media stack configuration with NFS and Docker services

- Added configuration for media stack on r5500, including paths for Jellyfin, Sonarr, Radarr, and other media services.
- Integrated NFS client for accessing Jellyfin libraries from nixdesk.
- Established Docker services for Dispatcharr and Organizr, including necessary user and group setups.
- Created systemd services for managing media directories and ensuring proper permissions.

modules/hosts/r5500/_services/qbittorrent.nix

@@ -0,0 +1,43 @@
+{ lib, mediaStackPaths, ... }:
+let
+  webPort = 8081;
+  btPort = 51413;
+  inherit (mediaStackPaths) downloadsDir downloadsIncompleteDir qbittorrentDataDir;
+in
+{
+  services.qbittorrent = {
+    enable = true;
+    openFirewall = true;
+    webuiPort = webPort;
+    torrentingPort = btPort;
+  };
+
+  users.groups.qbittorrent = { };
+  users.users.qbittorrent = {
+    isSystemUser = true;
+    group = "qbittorrent";
+    extraGroups = [ "media" ];
+    home = qbittorrentDataDir;
+  };
+
+  fileSystems."/var/lib/qbittorrent" = {
+    device = qbittorrentDataDir;
+    fsType = "none";
+    neededForBoot = false;
+    options = [
+      "bind"
+      "nofail"
+      "x-systemd.after=mnt-media\\x2dmedia\\x2dstack.mount"
+    ];
+  };
+
+  networking.firewall.allowedTCPPorts = [ webPort btPort ];
+  networking.firewall.allowedUDPPorts = [ btPort ];
+
+  # Default save path for new torrents (existing qBittorrent.conf may override after migration).
+  systemd.services.qbittorrent.preStart = lib.mkAfter ''
+    mkdir -p ${downloadsDir} ${downloadsIncompleteDir}
+    chmod 2775 ${downloadsDir} ${downloadsIncompleteDir}
+    chgrp media ${downloadsDir} ${downloadsIncompleteDir}
+  '';
+}