refactor: migrate to template-based theme system, clean up old per-theme configs

- Remove per-theme app configs (alacritty, foot, ghostty, hyprland,
  hyprlock, mako, rofi, swayosd, tmux, walker, waybar, etc.) now
  handled by default/themed/ templates
- Update omarchy scripts (bg-next, list, set) for new template flow
- Update configs: bootstrap, nvim, rofi, tmux, mako
- Tweak installers (02-install-base.sh, btop, desktop, goose, nvim,
  obsidian, theme, tmux)
- Remove obsolete hyprland-rofi-* and hyprland-walker-* scripts
- Update neovim.lua across remaining themes

installer/desktop.sh

@@ -4,7 +4,7 @@ if [[ -x "$(command -v systemctl)" ]]; then
     systemctl --user enable --now syncthing
 fi
 
-THEMES_DIR="${HOME}/.local/share/themes"
+THEME_DIR="${HOME}/.config/omarchy/current/theme"
 
 ${DOTFILES_DIR}/sync-config config/hypr
 
@@ -24,11 +24,11 @@ fi
 ${DOTFILES_DIR}/sync-config config/rofi
 
 ${DOTFILES_DIR}/sync-config config/mako
-ln -snf ${THEMES_DIR}/current/theme/mako.ini ${HOME}/.config/mako/config
+ln -snf ${THEME_DIR}/current/theme/mako.ini ${HOME}/.config/mako/config
 
 
 ${DOTFILES_DIR}/sync-config config/ghostty
-ln -snf ${THEMES_DIR}/current/theme/ghostty ${HOME}/.config/ghostty/theme
+ln -snf ${THEME_DIR}/current/theme/ghostty ${HOME}/.config/ghostty/theme
 
 
 ${DOTFILES_DIR}/sync-config config/chromium-flags.conf