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/hypr/default.nix

@@ -1,7 +1,7 @@
 {
   pkgs,
-  lib,
   config,
+  theme,
   ...
 }:
 
@@ -58,9 +58,9 @@ in
     enable = true;
 
     settings = {
-      background-color = "#1c1b1bee";
-      text-color = "#e5e2e1";
-      border-color = "#cffc00";
+      background-color = "${theme.colors.glassBg}ee";
+      text-color = theme.colors.textSecondary;
+      border-color = theme.colors.accentVolt;
       border-size = 1;
       border-radius = 0;
       width = 420;
@@ -73,13 +73,13 @@ in
       max-icon-size = 48;
 
       "urgency=critical" = {
-        border-color = "#ff7a59";
-        text-color = "#ffffff";
+        border-color = theme.colors.accentCoral;
+        text-color = theme.colors.textPrimary;
         default-timeout = 0;
       };
       "urgency=low" = {
-        border-color = "#2a2929";
-        text-color = "#adaaaa";
+        border-color = theme.colors.surfaceVariant;
+        text-color = theme.colors.textMuted;
       };
     };
   };