Function run_learn 

pub fn run_learn(
    command: &str,
    output: &str,
    exit_code: i32,
) -> Result<(), Error>

Run the learn flow: call LLM, validate + save pattern.

Loads configuration from environment, calls the LLM to generate a pattern, validates the result, and saves the pattern to disk. Retries up to 2 times if the LLM returns invalid TOML.