Allowed Scopes: experimental:chart-of-accounts:write

Partially updates one or more existing accounts by id. Updates are best-effort: each account is patched independently, successful updates are returned in accounts, and per-item failures are returned in failed so callers can retry only the failed ids. Use PUT /v1/experimental/accounts for bulk upsert by type and PUT /v1/experimental/accounts/set-purpose to assign account purposes.