Function load_config 

pub fn load_config<T>(
    config_path: Option<&str>,
    env_prefix: &str,
) -> Result<T, ConfigError>
where
    T: Default + DeserializeOwned + ApplyFlatEnv + Normalize,

Load config with full cascade: YAML -> figment env -> flat env -> normalise.

This replaces the copy-pasted Config::load() functions across DFE services. It orchestrates:

1. .env loading (via dotenvy, handled by config::setup)
2. YAML file discovery and loading
3. Figment env var merging (double-underscore nesting)
4. Flat env overrides (single-underscore, K8s-friendly)
5. Normalisation (infer implied settings)

Errors

Returns a ConfigError if config loading or deserialisation fails.