Delete stub rainbow_agent.rs (fake select_action, hardcoded train loss) and promote rainbow_agent_impl.rs to rainbow_agent.rs. Unify on the real 8-field RainbowAgentMetrics from rainbow_config.rs, replacing the 4-field stub version (epsilon→exploration_rate, average_loss→current_loss). 5 files changed: -667/+447 lines, 2698+32 tests pass, 0 clippy. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>