List Block Contracts

The caller's own active Block contracts for the Block Admin Dashboard's Active Contracts section (E1). Client-scoped by user.client_id (never input) and CLIENT-SAFE — no Stripe ids. Keyed by block_request_id so the UI joins it onto the request row it already renders.

Block-Admin only: contract billing detail (amounts, invoice status) is admin-facing, matching the rest of this dashboard and the UI's isBlockAdmin tab gate — a plain Block user must not read it via the API.