Function build_privilege_command 

pub fn build_privilege_command(tool: PrivilegeTool, command: &str) -> String

What: Build a privilege-escalated command string.

Inputs:

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

Output: Shell string like "sudo pacman -S foo" or "doas pacman -S foo".

Details: Simple prefix — does not handle password piping.