Add generic Codex-directed evolution execution

[nerdsane]

Summary

• add Codex-powered candidate mutation and generic campaign-plan execution for directed evolution
• gate live releases on executed native evaluator evidence bound to immutable Genesis refs
• keep Agent Answers as a convenience demo while moving metrics, traffic, generations, capabilities, evaluator namespace and release controls into campaign data

Verification

• cargo fmt --check
• cargo test -p paw-codex-worker -- --nocapture
• live plan-driven two-generation proof completed using Codex-generated Temper-native candidates, frozen evaluator evidence, pause, and rollback
• negative live run correctly rejects execution when frozen evaluator evidence is absent

[rita-aga]

Superseded by the WorkItem/WorkerRun Directed Evolution architecture now on main. Effort continues in #393.