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/_rotterdam/boot.nix

@@ -0,0 +1,31 @@
+{ pkgs, ... }:
+
+let
+  qubesnsh = pkgs.writeTextFile {
+    name = "qubes.nsh";
+    text = "HD1f65535a1:EFI\\qubes\\grubx64.efi";
+  };
+in
+
+{
+  boot = {
+    kernelParams = [
+      "processor.max_cstate=1" # Fixes bug where ryzen cpus freeze when in highest C state
+      "clearcpuid=514"
+      "amdgpu.ppfeaturemask=0xfffd3fff" # Fixes amdgpu freezing
+    ];
+    # QubesOS boot entry
+    loader.systemd-boot = {
+      extraFiles = {
+        "efi/edk2-shell/shell.efi" = "${pkgs.edk2-uefi-shell}/shell.efi";
+        "qubes.nsh" = qubesnsh;
+      };
+      extraEntries."qubes.conf" = ''
+        title Qubes OS
+        efi /efi/edk2-shell/shell.efi
+        options -nointerrupt qubes.nsh
+        sort-key ab
+      '';
+    };
+  };
+}