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

flake.nix

@@ -44,6 +44,7 @@
     inputs:
     let
       system = "x86_64-linux";
+      theme = import ./home/theme.nix;
 
       commonModules = [
         ./modules/core
@@ -56,7 +57,10 @@
             home-manager = {
               useGlobalPkgs = true;
               useUserPackages = true;
-              extraSpecialArgs = { inherit inputs; };
+              extraSpecialArgs = {
+                inherit inputs theme;
+                my = config.my;
+              };
               backupFileExtension = "backup";
               users.${config.my.username} = import ./home;
             };