Operator-run tooling that moves durable Cloudflare KV data into the live
AWS DynamoDB table, plus a runtime swap of the `value` attribute from
Binary to String so payloads are human-readable in the AWS console.
- cmd/migrate_cf_data: subcommands inventory, kv-import (idempotent via
attribute_not_exists), trading-audit-dump, convert-value-to-string
- internal/migration: policy allowlist, CF KV+D1 REST clients, DynamoDB
writer, report formatter with per-prefix counts + tests
- internal/storage/dynamodb_kv.go: Put writes MemberS, Get reads MemberS;
dropped empty-bytes sentinel (DynamoDB allows empty strings)
