The `_load_api_key()` function in longmemeval_bench.py and locomo_bench.py
searched for API keys in a fixed path (`~/.config/lu/keys.json`) using
personal key names (`anthropic_milla`, `anthropic_claude_code_main`).
This leaks internal infrastructure details into the public codebase and
trains contributors to store credentials in a non-standard location
rather than using the standard ANTHROPIC_API_KEY env var.
Simplified to: CLI flag > env var > empty string. Updated help text
and HYBRID_MODE.md docs to match.
Co-authored-by: Tadao <tadao@travisfixes.com>