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/starship/starship.toml

@@ -6,22 +6,22 @@ format = "$os$directory$git_branch$git_status$nix_shell$rust$c$python$cmd_durati
 
 [os]
 disabled = false
-style = "bold #e5e2e1"
+style = "bold @text@"
 symbols = { NixOS = "󱄅 " }
 
 [directory]
 truncation_length = 3
 truncate_to_repo = true
-style = "bold #CFFC00"
+style = "bold @volt@"
 format = "[ $path]($style) "
 
 [git_branch]
 symbol = " "
-style = "bold #00BFFF"
+style = "bold @blue@"
 format = "on [$symbol$branch]($style) "
 
 [git_status]
-style = "bold #FF7A59"
+style = "bold @coral@"
 format = "([$all_status$ahead_behind]($style) )"
 conflicted = " "
 ahead      = " "
@@ -30,35 +30,35 @@ diverged   = " "
 untracked  = " "
 stashed    = " "
 modified   = " "
-staged     = " [](bold #CFFC00)"
+staged     = " [](bold @volt@)"
 renamed    = " "
 deleted    = " "
 
 [nix_shell]
 symbol = " "
-style = "bold #e3ff66"
+style = "bold @voltLight@"
 format = "via [$symbol$state]($style) "
 
 [rust]
 symbol = " "
-style = "bold #e3ff66"
+style = "bold @voltLight@"
 format = "[$symbol($version )]($style)"
 
 [c]
 symbol = " "
-style = "bold #00BFFF"
+style = "bold @blue@"
 format = "[$symbol($version )]($style)"
 
 [python]
 symbol = " "
-style = "bold #CFFC00"
+style = "bold @volt@"
 format = "[$symbol($version )]($style)"
 
 [cmd_duration]
 min_time = 2000
-style = "bold #FF7A59"
+style = "bold @coral@"
 format = "[  $duration]($style) "
 
 [character]
-success_symbol = "[❯ ](bold #CFFC00) "
-error_symbol = "[❯ ](bold #FF7A59) "
+success_symbol = "[❯ ](bold @volt@) "
+error_symbol = "[❯ ](bold @coral@) "