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/_io/hardware-configuration.nix

@@ -0,0 +1,37 @@
+{
+  config,
+  lib,
+  modulesPath,
+  inputs,
+  ...
+}:
+
+{
+  imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+
+  boot = {
+    initrd = {
+      availableKernelModules = [
+        "xhci_pci"
+        "ahci"
+        "usb_storage"
+        "sd_mod"
+        "sdhci_pci"
+      ];
+    };
+    kernelModules = [ "kvm-intel" ];
+  };
+
+  zramSwap = {
+    enable = true;
+    memoryPercent = 100;
+  };
+
+  powerManagement.cpuFreqGovernor = lib.mkDefault "powersave";
+
+  networking.useDHCP = lib.mkDefault true;
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+
+  hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
+}