Cross-provider positions + USD value for an arbitrary wallet

One call fans out to every supported provider for `user`. Polymarket returns the position array + total USDC value; Hyperliquid returns `clearinghouseState` (perp positions, margin, equity). `summary.totalValueUsd` sums providers that exposed a number — providers that didn't (or upstream failed) appear in `warnings`. Pass `?provider=polymarket,hyperliquid` to fan out only to specific providers; omit for all.