[Router] AuditSink — CloudEvents JSONL (M10)

[ramkrishna2910]

Goal

AuditSink (module M10) — persist every decision.

Scope

• Append one CloudEvents JSONL record per decision to route_audit.jsonl (schema from the audit-schema issue).
• Input hashed by default.
• Wired into the dispatch path.

Acceptance

Each routed request emits exactly one schema-valid CloudEvents line; input_hash present; no raw input unless opt-in flag set.

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Depends on: #2385, #2377