Chain-derived cumulative P&L timeseries from closed_positions_cache.

Polymarket user-pnl-api starts measurements from when they indexed the wallet — for inactive whales like Theo4 (last trade Nov 2024) it returns only the post-peak plateau, missing the ramp-up. closed_positions_cache has every closed position with its actual close timestamp and realized PnL, so we can reconstruct the real growth curve.

Daily-bucketed cumulative sum. Returns {address, source: "chain", points: [{t: unix_ts, p: cumulative_pnl}, ...]}.

Coverage: ~3K wallets in cache (top earners + active syncs). Wallets not in cache return empty points — frontend should fall back to Polymarket user-pnl-api.