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/.config/hypr/hypridle.conf

@@ -0,0 +1,16 @@
+general {
+    lock_cmd = pidof hyprlock || hyprlock
+    before_sleep_cmd = pidof hyprlock || hyprlock
+    after_sleep_cmd = hyprctl dispatch dpms on
+}
+
+listener {
+    timeout = 600
+    on-timeout = pidof hyprlock || hyprlock
+}
+
+listener {
+    timeout = 900
+    on-timeout = hyprctl dispatch dpms off
+    on-resume = hyprctl dispatch dpms on
+}