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/rofi/volt.rasi

@@ -2,15 +2,15 @@
 // Flat brutalist-glass: dark glass surfaces, volt-lime selection, 0 radius.
 
 * {
-    bg0: rgba( 14, 14, 14, 95 % );
-    bg1: rgba( 28, 27, 27, 95 % );
-    fg0: #e5e2e1;
-    fg1: #ffffff;
-    fg2: #adaaaa;
-    volt: #CFFC00;
-    volt-dim: rgba( 207, 252, 0, 10 % );
-    coral: #FF7A59;
-    border0: rgba( 255, 255, 255, 8 % );
+    bg0: @bg0@;
+    bg1: @bg1@;
+    fg0: @fg0@;
+    fg1: @fg1@;
+    fg2: @fg2@;
+    volt: @volt@;
+    volt-dim: @voltDim@;
+    coral: @coral@;
+    border0: @border0@;
 
     background-color: transparent;
     text-color: @fg0;