Get user vault state and active positions

Vault state with active position summaries (GET /v1/vault response). Returns the caller's bettor-side vault (owner_type='user') when one exists; falls back to their maker-side vault (owner_type='mm') for pure-MM accounts so the portfolio surface reflects every USDC the caller controls. positions is the bettor-side active list when returning the user vault, or the maker-side active list (joined via q.market_maker_id) when returning the MM vault.