Function component_value_to_tier 

pub fn component_value_to_tier(
    value: &str,
    harness: &str,
    model_config: &ModelConfig,
) -> Option<Tier>

Resolve a <!-- agent:model --> component value to a Tier.

Accepts tier names (auto|low|med|high) or concrete model names (resolved via the harness’s tier map). Returns None if the value is unrecognized.