Emits the request-level audit record to structured logs (scraped by the
existing alloy/loki substrate) and surfaces security events at warn
level. Placeholder behind the AuditSink interface — the classification-
aware loki+buffer+reconcile sink (confidential fails closed, internal
degrades) lands in #54 and replaces this without touching callers.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
