home: centralize theme and make home-manager feature-aware

- add home/theme.nix as the single Silicon Volt palette and pass it to
  home modules via extraSpecialArgs
- drive foot, hyprland, hyprlock, mako, fzf, starship, rofi and the
  herdr picker from that palette; raw config files use @color@ tokens
  substituted at build time
- pass my = config.my into home-manager; add my.pi.enable, my.flakeDir
- gate home/pi.nix on my.pi.enable (enabled on hades)
- route zshconf/hyprconf aliases and FLAKE_CONFIG through my.flakeDir
- rename the hyprland monitor option volt.monitors -> hypr.monitors
- fix use_auto_tmux command-substitution bug in zsh/init.zsh
- track home/nvim/config/lazy-lock.json for reproducible plugins
- document theming and toggles in the README

home/zsh/init.zsh

@@ -18,7 +18,7 @@ fi
 
 # Auto-tmux configuration
 use_auto_tmux () {
-    ! ([ -z "$DISPLAY" ] && [ -z "$WAYLAND_DISPLAY" ] || $(pgrep -x "i3" > /dev/null || pgrep -x "sway" > /dev/null || pgrep -x "Hyprland" > /dev/null))
+    ! ([ -z "$DISPLAY" ] && [ -z "$WAYLAND_DISPLAY" ] || pgrep -x i3 >/dev/null || pgrep -x sway >/dev/null || pgrep -x Hyprland >/dev/null)
 }
 
 if use_auto_tmux; then