feat: zsh default shell + starship/bat/eza/zoxide shell experience

zsh is now the default login shell (programs.zsh.enable +
users.defaultUserShell, mkOverride 500 to beat bash.nix's mkDefault;
per-user shell= still overrides). modules/home/shell.nix configures the
interactive experience (nomarchy.shell.enable):

- zsh: completion, autosuggestions, syntax highlighting, big shared
  history, autocd.
- starship prompt themed from the palette (a `nomarchy` palette built
  from theme-state.json colors).
- bat as cat (theme "ansi" → tracks the terminal/theme palette), eza as
  ls (icons + git + dirs-first), zoxide as cd (--cmd cd).
- rg/fd shipped as themselves — deliberately NOT aliased over grep/find
  (flag differences surprise).

home.shell.enableZshIntegration = true is the single lever; starship,
eza, zoxide, ghostty and yazi all emit their zsh hooks from it (no
per-module edits). Verified: flake check green, default shell resolves
to zsh, .zshrc carries the starship/zoxide/eza/yazi hooks + aliases,
starship palette renders, all tools in the live ISO closure.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/home/shell.nix

@@ -0,0 +1,114 @@
+# Shell experience — zsh (the default login shell, set system-side) with
+# autosuggestions + syntax highlighting, a themed starship prompt, and
+# modern CLI tools wired in: bat (cat), eza (ls), zoxide (cd). bat uses
+# the "ansi" theme so it follows the terminal palette (Ghostty is themed
+# from the same JSON); starship is themed from the palette directly.
+#
+# home.shell.enableZshIntegration = true is the single lever that makes
+# every integrating program (starship, eza, zoxide, ghostty, yazi) emit
+# its zsh hooks — no per-module flags needed.
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.nomarchy;
+  t = cfg.theme;
+  c = t.colors;
+in
+{
+  config = lib.mkIf cfg.shell.enable {
+    home.shell.enableZshIntegration = true;
+
+    # rg/fd as themselves (NOT aliased over grep/find — their flags
+    # differ enough to surprise). Available regardless of yazi/rofi.
+    home.packages = with pkgs; [ ripgrep fd ];
+
+    programs.zsh = {
+      enable = true;
+      enableCompletion = true;
+      autosuggestion.enable = true;
+      syntaxHighlighting.enable = true;
+      autocd = true;
+      history = {
+        size = 50000;
+        save = 50000;
+        ignoreDups = true;
+        ignoreSpace = true;
+        expireDuplicatesFirst = true;
+      };
+      shellAliases = {
+        cat = "bat --paging=never";
+        less = "bat";
+        grep = "grep --color=auto";
+        # eza enableZshIntegration aliases ls/ll/la; add a couple extras.
+        lt = "eza --tree --level=2 --icons=auto --group-directories-first";
+        tree = "eza --tree --icons=auto --group-directories-first";
+        ".." = "cd ..";
+        "..." = "cd ../..";
+      };
+    };
+
+    programs.starship = {
+      enable = true;
+      settings = {
+        add_newline = false;
+        palette = "nomarchy";
+        # starship wants full #rrggbb (or names) — keep the leading #.
+        palettes.nomarchy = {
+          inherit (c) base text accent good warn bad subtext;
+        };
+        format = lib.concatStrings [
+          "[](accent)"
+          "$directory"
+          "$git_branch$git_status"
+          "$character"
+        ];
+        directory = {
+          style = "fg:text bg:accent";
+          format = "[ $path ]($style)";
+          truncation_length = 3;
+          truncate_to_repo = true;
+        };
+        git_branch = {
+          style = "fg:base bg:warn";
+          format = "[ $symbol$branch ]($style)";
+          symbol = " ";
+        };
+        git_status = {
+          style = "fg:base bg:warn";
+          format = "[$all_status$ahead_behind ]($style)";
+        };
+        character = {
+          success_symbol = "[ ❯](good)";
+          error_symbol = "[ ❯](bad)";
+        };
+        cmd_duration = {
+          min_time = 2000;
+          style = "fg:subtext";
+          format = "[  $duration ]($style)";
+        };
+      };
+    };
+
+    # bat: "ansi" follows the terminal's 16-color palette → tracks the
+    # active Nomarchy theme (Ghostty bakes it) with no per-theme config.
+    programs.bat = {
+      enable = true;
+      config = {
+        theme = "ansi";
+        style = "numbers,changes,header";
+      };
+    };
+
+    programs.eza = {
+      enable = true;
+      icons = "auto";
+      git = true;
+      extraOptions = [ "--group-directories-first" ];
+    };
+
+    programs.zoxide = {
+      enable = true;
+      options = [ "--cmd cd" ]; # `cd` becomes the smart jumper (z under the hood)
+    };
+  };
+}