Batch traceability

Public summary for a batch leg or full custody chain (TC-XXXXXXXX-*). Use ?id= with a leg (TC-XXXXXXXX-YYYY) or short chain key (TC-XXXXXXXX), or ?chain=TC-XXXXXXXX. Each event recomputes SHA256(image + batch_id + GPS + event_id) from IPFS and compares it to the stored data_hash.