Clarified the archive-portfolio description

Broker API

Clarifies the description for archiving (soft-deleting) a portfolio. Archiving is only permitted when the portfolio has no active subscriptions, and archived portfolios are hidden from the default list response and cannot be used for new subscriptions. Removes the misleading note that inactive portfolios cannot be added as weights to new portfolios.

Affected Endpoints

• DELETE /v1/rebalancing/portfolios/{portfolio_id}