use same shell setup as in nix home manager

roles/pi_modern_shell_env/defaults/main.yml

@@ -12,9 +12,9 @@ pi_modern_shell_env_packages:
   - tmux
   - curl
 
-# Bookworm's apt coverage for starship is inconsistent across releases/
-# arches, so it's installed via the official install script instead.
-pi_modern_shell_env_starship_install_url: https://starship.rs/install.sh
+# oh-my-posh isn't packaged in apt; installed via the official script
+# instead, matching the prompt used in ~/nixconfig's home-manager setup.
+pi_modern_shell_env_ohmyposh_install_url: https://ohmyposh.dev/install.sh
 
 pi_modern_shell_env_target_user: "{{ main_user | default('root') }}"