refactor(shells): use native Home Manager Nushell and Nushell login on non-desktop hosts (#513)

* refactor(shells): use native Home Manager Nushell environment

Replace the Bash login-shell wrapper and hand-maintained Nushell PATH with programs.nushell.loadSessionVariables and home.sessionPath. Launch Nushell directly from Kitty, Ghostty, and Zed, with the macOS config-home override and Ghostty's vendor autoload directory.

Upstream feature: https://github.com/nix-community/home-manager/pull/9666

Assisted-by: DeepSeek Harness (deepseek-flash)

* feat(hosts): use Nushell as login shell on Ruby and Kana

Set the per-user shell explicitly and add Nushell to the system shell list. The system default shell and root remain unchanged.

Assisted-by: DeepSeek Harness (deepseek-flash)

* fix(ssh): preserve tuios session marker across SSH

Forward TUIOS_SESSION and accept it on NixOS sshd, so an SSH session opened from inside tuios does not auto-attach a nested remote tuios.

Assisted-by: DeepSeek Harness (deepseek-flash)

* feat(nixos): use Nushell login shell on non-desktop hosts

Enable the Nushell login shell through a shared module imported by the server and agent profiles. Desktop profiles continue to use Bash.

Assisted-by: DeepSeek Harness (deepseek-flash)

* fix(tuios): skip auto-attach in SSH sessions

Remote interactive shells now stay plain Nushell instead of starting a nested TUIOS when the SSH client is already inside a local TUIOS session. Local TUIOS auto-start is unchanged.

Assisted-by: DeepSeek Harness (deepseek-flash)

home/darwin/shell.nix

@@ -1,22 +1,14 @@
-{ config, lib, ... }:
-let
-  envExtra = ''
-    export PATH="/opt/homebrew/bin:/usr/local/bin:$PATH"
-  '';
-in
+{ config, ... }:
 {
-  # Homebrew's default install location:
-  #   /opt/homebrew for Apple Silicon
-  #   /usr/local for macOS Intel
-  # The prefix /opt/homebrew was chosen to allow installations
-  # in /opt/homebrew for Apple Silicon and /usr/local for Rosetta 2 to coexist and use bottles.
-  programs.bash = {
-    enable = true;
-    bashrcExtra = lib.mkAfter envExtra;
-  };
+  # Homebrew install locations for Apple Silicon and Intel.
+  home.sessionPath = [
+    "/opt/homebrew/bin"
+    "/usr/local/bin"
+  ];
+
+  programs.bash.enable = true;
   programs.zsh = {
     enable = true;
     dotDir = "${config.xdg.configHome}/zsh";
-    inherit envExtra;
   };
 }