Function ensure_api_key_for_large_file 

pub fn ensure_api_key_for_large_file(
    file_size: u64,
    config: &CliConfig,
) -> Result<()>

Check if a file exceeds the free tier limit and require API key if so

Returns Ok(()) if:

• File is under 1GB (no API key required)
• File is over 1GB AND API key is configured with valid paid plan

Returns error if file is over 1GB and no API key/paid plan