Consolidate the egress-policy code into a dedicated `security/egress/` subpackage (`policy.py` + `audit_hook.py`) with a README documenting the design, scope model, and the full map of enforcement points. No behavior change — module paths moved from `security.egress_policy` / `security.egress_audit_hook` to `security.egress.policy` / `security.egress.audit_hook`.
