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).

services/desktop/desktop-hyprland.nix

@@ -0,0 +1,36 @@
+{ pkgs, ... }:
+
+# Hyprland (wayland) desktop: compositor, login manager, audio, portals.
+# Reusable for any host that wants a local GUI session (currently: terra).
+{
+  programs.hyprland.enable = true;
+
+  services.greetd = {
+    enable = true;
+    settings.default_session.command =
+      "${pkgs.tuigreet}/bin/tuigreet --time --cmd Hyprland";
+  };
+
+  # Audio (pipewire replaces pulseaudio/jack).
+  security.rtkit.enable = true;
+  services.pipewire = {
+    enable = true;
+    alsa.enable = true;
+    pulse.enable = true;
+  };
+
+  # Screen-share / file-picker portals for wayland apps.
+  xdg.portal = {
+    enable = true;
+    extraPortals = [ pkgs.xdg-desktop-portal-hyprland ];
+  };
+
+  hardware.graphics.enable = true;   # OpenGL/Vulkan for the compositor + apps
+  services.libinput.enable = true;
+
+  environment.systemPackages = with pkgs; [
+    alacritty
+  ];
+
+  networking.networkmanager.enable = true;
+}