Get Publisher Portfolio Coverage

Verified trades from a publisher's linked brokerage accounts (Plaid).

Brokerage trades are private: no publisher has opted in to publishing them, so everyone else gets counts only (total_stocks, total_transactions) and an empty coverage. The publisher themselves gets the coverage list with each trade's date, ticker and side; quantities, prices, amounts and P&L are never returned.

Args: publisher_id: Publisher UUID or username