Function resolve_input 

pub fn resolve_input(
    path_str: &str,
) -> Result<(PathBuf, Option<TempModelFile>), CliError>

Resolve an input path: if “-”, read stdin to tempfile; otherwise return the path as-is.

Returns (resolved_path, Option<TempModelFile>). The caller must hold the TempModelFile in scope to prevent premature cleanup.