docs: evidenceId/claimId uniqueness semantics unstated in reviewed-extraction-evidence

[briananderson1222]

First-consumer doc gap (kontourai/fieldwork#88): neither the .d.ts nor README states that evidenceId must be unique per bundle while claimId may legitimately recur across evidence entries pointing at one claim (the many-items-decide-one-field-consistently case). The consumer had to derive this from first principles; a one-line JSDoc note on each field would close it.

https://claude.ai/code/session_011t2tM3Bu8MVAMQnrovGR6m