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/jellyfin.nix

@@ -0,0 +1,29 @@
+# Jellyfin on r5500. Local libraries: /mnt/media-stack/jellyfin/{movies,tv}.
+# Bulk libraries: /mnt/nixdesk-jellyfin/{movies,tv} (NFS from 14900k).
+{ lib, ... }:
+{
+  nixpkgs.overlays = [
+    (final: prev: {
+      jellyfin-web = prev.jellyfin-web.overrideAttrs (oldAttrs: {
+        postInstall =
+          (oldAttrs.postInstall or "")
+          + ''
+            find "$out" -type f \( -name 'banner-light.*.png' -o -name 'banner-dark.*.png' \) \
+              -exec truncate -s 0 {} \;
+          '';
+      });
+    })
+  ];
+
+  users.users.jellyfin.extraGroups = [ "media" ];
+
+  services.jellyfin = {
+    enable = true;
+    openFirewall = true;
+  };
+
+  systemd.services.jellyfin.serviceConfig = {
+    SupplementaryGroups = [ "media" ];
+    PrivateUsers = lib.mkForce false;
+  };
+}