Reorganize desktop roles: extract common bootstrap and host-specific layers

- Add profile_desktop_common with shared desktop bootstrap (emptty, PAM,
  dotfiles, templates, GPG, Maildir, Flatpak, st, external tools)
- Add profile_desktop_host with host-specific tasks (NVIDIA/PRIME on nymph)
- Reduce profile_desktop_i3 to i3/X11-only tasks
- Create profile_desktop_hyprland for Hyprland Wayland session
- Add dual-session support (i3 + Hyprland) on nymph with session choice
- Create shared Hyprland/Waybar dotfiles under dotfiles/desktop/
- Fix Waybar: bottom position, no persistent workspaces, sort by number
- Rename host_dotfiles to host_i3_dotfiles for clarity
- Make emptty restart manual by default to avoid session drops

dotfiles/desktop/.local/bin/screenshot-wayland

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+set -eu
+
+mode=${1:-full}
+target_dir="$HOME/Pictures/Screenshots"
+target_file="$target_dir/$(date +%Y-%m-%d-%H%M%S).png"
+
+mkdir -p "$target_dir"
+
+case "$mode" in
+  full)
+    grim "$target_file"
+    ;;
+  region)
+    grim -g "$(slurp)" "$target_file"
+    ;;
+  output)
+    grim -g "$(slurp -o)" "$target_file"
+    ;;
+  *)
+    printf 'Usage: %s [full|region|output]\n' "$0" >&2
+    exit 1
+    ;;
+esac
+
+if command -v wl-copy >/dev/null 2>&1; then
+  wl-copy < "$target_file"
+fi
+
+if command -v notify-send >/dev/null 2>&1; then
+  notify-send "Screenshot saved" "$target_file"
+fi