List interaction receipts

Verified-interaction proofs across the account, newest first. source says which store answered: receipt_index is the normal path, with real pagination; legacy_scan serves an account whose receipts all predate that index by filtering the audit log, which can return EMPTY pages mid-walk. On either source, follow the cursor until it is null before concluding there are none. The two are never merged, and a cursor always resumes on the source that issued it.