Create Business portfolio items for many completed searches.

Request-level authorization and group lookup failures still fail the
full request. Per-search failures are returned in errors so the
caller can add every eligible row from a checkbox selection without
retrying successful rows.

Bulk success and error rows are intentionally lightweight. The
frontend only needs IDs and stable error codes for row correlation,
cache refreshes, and summary toasts, so the endpoint avoids full
PortfolioItem serialization and verbose per-row errors.