feat: add workspace usage attribution (#339)

* feat: add workspace usage attribution

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* fix: address workspace attribution review

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* docs(trail): record PR 339 review completion

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* fix(engine): redact observer provenance identity

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* docs(trail): align PR 339 rebased provenance

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* docs(trail): record PR 339 replacement review

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* docs: align attribution migration contract

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486

* docs(trail): record late PR 339 follow-ups

Session-Id: 01a018b2-009d-7e61-9101-06ef63fa2486