Function build_cli_error 

pub fn build_cli_error(message: &str, hint: Option<&str>) -> Event

Build a CLI error event with optional hint.

Equivalent to: json_error("cli_error", message).hint_if_some(hint).build()

Always returns an event with:

• code: “cli_error”
• retryable: false
• trace: {}

Panics if message is empty (required by protocol contract).