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/_trantor/fail2ban.nix

@@ -0,0 +1,23 @@
+{ config, pkgs, ... }:
+
+{
+  services.fail2ban = {
+    enable = true;
+    maxretry = 5;
+    ignoreIP = [
+      "127.0.0.0/8"
+      "::1"
+      "10.0.0.0/8"
+      "172.16.0.0/12"
+      "192.168.0.0/16"
+      "100.64.0.0/10"
+    ];
+    bantime = "1h";
+    bantime-increment = {
+      enable = true;
+      multipliers = "1 2 4 8 16 32 64";
+      maxtime = "10000h";
+      overalljails = true;
+    };
+  };
+}