terra: add Ryzen 9 5900X desktop (Hyprland, tailnet, dev tools)

Replaces CachyOS on the OS SSD (Kingston SA400, disko-managed). Dev-data
disks (sdc ext4 /mnt/hdd_01, LVM vg_ssd /mnt/ssd_01) stay out of disko and
are mounted as plain filesystems so they're never wiped. Desktop split into
services/desktop/desktop-hyprland.nix (session: compositor, greeter, audio,
portals) and desktop-apps.nix (things darman actually launches, including
claude-code — allowlisted alongside the other unfree desktop apps).

hosts/terra/hardware-configuration.nix

@@ -0,0 +1,22 @@
+# PLACEHOLDER — replaced on install.
+#
+# disko (disk-config.nix) owns "/" and "/boot", so this file only carries
+# kernel modules + platform. nixos-anywhere regenerates it via:
+#   nixos-generate-config --no-filesystems
+# Standard AMD desktop (SATA SSD, NVMe present but unused) — the generator
+# should get ahci/nvme right on its own; these are a sane fallback so stage-1
+# still mounts root if it doesn't.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  boot.initrd.availableKernelModules = [ "ahci" "xhci_pci" "usb_storage" "usbhid" "sd_mod" "nvme" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ "kvm-amd" ];
+  boot.extraModulePackages = [ ];
+
+  # NO fileSystems here — disko defines "/" and "/boot".
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+}