Starship: explicit left format plus right_format = "$all" and headless render test

To keep the left prompt minimal and push language/cloud modules right, list left modules explicitly in format (ending with $line_break$character) and set right_format = "$all"; $all excludes modules already named in format, so nothing duplicates. Use a conditional group like ($username$hostname ) so the trailing space only appears when username/hostname render (ssh or root). To verify a home-manager starship config without rebuilding: nix eval --json the programs.starship.settings, convert with json2toml (remarshal), then STARSHIP_CONFIG=file starship prompt --cmd-duration 4000 and --right; set SSH_CONNECTION to simulate ssh. Strip %{ %} and ANSI escapes with sed to read the output.