Cumulative realized PnL curve over the last N days

Walks every fill on the caller org's wallets (filtered by optional `walletId`/`walletAddress`/`provider`), applies the same FIFO sell match used by `/v1/me/pnl`, and returns one cumulative-realized point per sell event within the window. The first and last timestamps of the window are always included so the chart spans the full requested range. `days` is clamped to [1, 30]. Sort/groupBy/cursor are NOT accepted — the curve is implicitly time-ordered.