Module credentials 

Credential resolution with a priority chain: env vars -> TOML config.

This replaces the old load_api_key_from_keyring() approach with a deterministic, testable resolver that does not depend on OS keyring.

Resolution order

Credential	1st (highest priority)	2nd	3rd (TOML fallback)
Anthropic API	ANTHROPIC_OAUTH_TOKEN	ANTHROPIC_API_KEY	credentials.anthropic_api_key
Hyperliquid key	HYPERLIQUID_PRIVATE_KEY	—	credentials.hyperliquid_private_key

Structs

CredentialResolver

Resolves credentials from environment variables and TOML config.