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/vaultwarden.nix

@@ -0,0 +1,26 @@
+{
+  config,
+  lib,
+  inputs,
+  ...
+}:
+let
+  utils = import ../../../utils.nix { inherit inputs lib; };
+  inherit (utils) mkNginxVHosts;
+in
+{
+  services.vaultwarden = {
+    enable = true;
+    config = {
+      DOMAIN = "https://pass.baduhai.dev";
+      SIGNUPS_ALLOWED = false;
+      ROCKET_ADDRESS = "127.0.0.1";
+      ROCKET_PORT = 58222;
+    };
+  };
+
+  services.nginx.virtualHosts = mkNginxVHosts {
+    domains."pass.baduhai.dev".locations."/".proxyPass =
+      "http://${config.services.vaultwarden.config.ROCKET_ADDRESS}:${toString config.services.vaultwarden.config.ROCKET_PORT}/";
+  };
+}