* 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)