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/configuration.nix

@@ -0,0 +1,47 @@
+{ config, pkgs, lib, ... }:
+
+# terra — Ryzen 9 5900X / Radeon RX 6800 XT desktop (MSI MS-7A32). Replaces
+# CachyOS on the OS SSD (Kingston SA400, sdb). Dev-data disks (sdc ext4
+# /mnt/hdd_01, LVM vg_ssd /mnt/ssd_01) are kept out of disko and mounted here
+# as plain filesystems so they're never wiped. The leftover ntfs disks
+# (sda, sdf, nvme0n1) are ignored entirely — not referenced anywhere.
+{
+  imports = [
+    ./hardware-configuration.nix
+    ./disk-config.nix          # disko: OS-disk (sdb) partitions + filesystems
+    ./secrets.nix               # sops-nix: darman password, tailscale key
+    ../../common.nix               # shared base: user / ssh / nix / firewall
+    ../../services/vpn/tailscale.nix
+    ../../services/desktop/desktop-hyprland.nix
+    ../../services/desktop/desktop-apps.nix
+  ];
+
+  networking.hostName = "terra";
+
+  # ---- home-manager (user-level config for darman) ----
+  home-manager.useGlobalPkgs = true;
+  home-manager.useUserPackages = true;
+  home-manager.backupFileExtension = "hm-bak";
+  home-manager.users.darman = import ./home.nix;
+
+  # ---- Boot (UEFI) ----
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+  hardware.cpu.amd.updateMicrocode = true;
+
+  # ---- Dev-data disks — NOT in disko, mounted read-write, never wiped ----
+  # UUIDs captured from the running CachyOS box; verify after install
+  # (`lsblk -o NAME,UUID,MOUNTPOINT`) in case disko/kernel enumerates differently.
+  fileSystems."/mnt/hdd_01" = {
+    device = "/dev/disk/by-uuid/b8445126-ec6d-4f88-818a-d9e13031d9a4";
+    fsType = "ext4";
+    options = [ "nofail" ];
+  };
+  fileSystems."/mnt/ssd_01" = {
+    device = "/dev/disk/by-uuid/6ca18a9f-27bc-4e58-aea8-de43a0d0ed5d";
+    fsType = "ext4";
+    options = [ "nofail" ];
+  };
+
+  system.stateVersion = "26.05";
+}