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/setup-gtk-theme

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+THEME="Yaru-blue-dark"
+ICONS="Yaru-blue-dark"
+CURSOR="Yaru"
+FONT_UI="Liberation Sans 10"
+
+mkdir -p "$HOME/.config/gtk-3.0"
+mkdir -p "$HOME/.config/gtk-4.0"
+
+cat > "$HOME/.config/gtk-3.0/settings.ini" <<EOF
+[Settings]
+gtk-theme-name=$THEME
+gtk-icon-theme-name=$ICONS
+gtk-cursor-theme-name=$CURSOR
+gtk-font-name=$FONT_UI
+gtk-application-prefer-dark-theme=1
+gtk-xft-antialias=1
+gtk-xft-hinting=1
+gtk-xft-hintstyle=hintslight
+gtk-xft-rgba=rgb
+EOF
+
+cat > "$HOME/.config/gtk-4.0/settings.ini" <<EOF
+[Settings]
+gtk-theme-name=$THEME
+gtk-icon-theme-name=$ICONS
+gtk-cursor-theme-name=$CURSOR
+gtk-font-name=$FONT_UI
+gtk-application-prefer-dark-theme=1
+EOF
+
+if command -v gsettings >/dev/null 2>&1; then
+  gsettings set org.gnome.desktop.interface gtk-theme "$THEME" >/dev/null 2>&1 || true
+  gsettings set org.gnome.desktop.interface icon-theme "$ICONS" >/dev/null 2>&1 || true
+  gsettings set org.gnome.desktop.interface cursor-theme "$CURSOR" >/dev/null 2>&1 || true
+  gsettings set org.gnome.desktop.interface color-scheme prefer-dark >/dev/null 2>&1 || true
+fi