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/btop.sh

@@ -1,9 +1,9 @@
 #!/bin/sh -e
 
 ${DOTFILES_DIR}/sync-config config/btop
-THEMES_DIR="${HOME}/.local/share/themes"
+THEME_DIR="${HOME}/.config/omarchy/current/theme"
 
 # theme link
 mkdir -p ~/.config/btop/themes
-ln -snf ${THEMES_DIR}/current/theme/btop.theme ${HOME}/.config/btop/themes/current.theme
+ln -snf ${THEME_DIR}/btop.theme ${HOME}/.config/btop/themes/current.theme