Function apply_cli_llm_overrides 

pub fn apply_cli_llm_overrides(
    cfg: &mut AppConfig,
    provider_arg: Option<&str>,
    model_arg: Option<&str>,
) -> EffectiveLlmConfig

Apply CLI-provided provider and/or model overrides to an in-memory config.

This is a convenience wrapper around apply_session_llm_overrides intended for thin adapters (CLI basic mode, CLI TUI) so they don’t re-implement precedence, provider/model compatibility checks, or provider-config creation.

The inputs map directly to CLI flags:

• provider_arg: --provider <provider> style argument (provider id)
• model_arg: --model <model> style argument (model id)

This function does not persist any changes to disk.