add aspects/hosts/ configurations

Host-specific NixOS configurations for:
- alexandria (server)
- io (desktop)
- rotterdam (desktop)
- trantor (server, aarch64)

Each host has a main config file and _hostname/ directory
with hardware-configuration and other host-specific modules.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

aspects/hosts/_alexandria/jellyfin.nix

@@ -0,0 +1,15 @@
+{ lib, inputs, ... }:
+let
+  utils = import ../../../utils.nix { inherit inputs lib; };
+  inherit (utils) mkNginxVHosts;
+in
+{
+  services.jellyfin = {
+    enable = true;
+    openFirewall = true;
+  };
+
+  services.nginx.virtualHosts = mkNginxVHosts {
+    domains."jellyfin.baduhai.dev".locations."/".proxyPass = "http://127.0.0.1:8096/";
+  };
+}