Function build_password_pipe 

pub fn build_password_pipe(
    tool: PrivilegeTool,
    password: &str,
    command: &str,
) -> Option<String>

What: Build a command that pipes a password to the privilege tool via stdin.

Inputs:

• tool: Resolved privilege tool.
• password: Cleartext password.
• command: The unprivileged command to wrap.

Output:

• Some(cmd) for tools that support stdin password (sudo).
• None for tools that do not (doas).

Details:

• Uses shell_single_quote for safe password escaping.
• Only sudo supports -S (read password from stdin).