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

ansible/roles/profile_desktop_hyprland/templates/Hyprland.desktop.j2

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Name=Hyprland
+Comment=Hyprland Wayland compositor
+Exec={{ user_home }}/.local/bin/start-hyprland-session
+TryExec=Hyprland
+Type=Application
+DesktopNames=Hyprland
+Keywords=wayland;wm;windowmanager;window;manager;tiling;compositor;