Audit endpoints

Status: stub. Day 3 deliverable.

Three read-only endpoints expose the Continuous Data Room (Doctrine §III).

Path	Returns
`GET /api/v1/audit/logs`	Every L2 decision result, scoped to the calling tenant.
`GET /api/v1/audit/policy-commits`	Authorship signatures (one row per `dsl_hash` ever committed).
`GET /api/v1/audit/l4-overrides`	Every L4 (Judgment UI) human override, with reason.

All three are tenant-scoped — there is no cross-tenant read path even for the platform operator.