List and query credit grants in the active scope

Returns the credit grants (coupons, promotions, support credits and prepaid top-ups) visible in the active tenant/subscription/project scope, as rendered by the Credits page on route load. Each grant carries its granted/consumed/remaining balances in ten-thousandths of the currency unit, its lifecycle status (active, exhausted, expired) and its ARN-style reference. This single endpoint also serves the search/filter/sort/paginate behavior (billing.credit.search_filter_sort): the UI exposes status chips (All / Active / Exhausted / Expired) which map to the status query parameter, and source narrows by grant origin; q, sort, order, page and pageSize apply standard collection semantics. Plain list = same call with no filter parameters. Validation: scopeId must reference a scope the caller can access (otherwise 403 FORBIDDEN); status must be one of active|exhausted|expired and source one of coupon|promo|support-credit|prepaid (otherwise 422 VALIDATION_FAILED); unknown sort keys map to 422 VALIDATION_FAILED. Async & state: Synchronous read; no state change. No SSE frames are emitted. Errors: 401 when unauthenticated; 403 when the caller lacks read access to the billing scope (reader and billing roles and above may read); 422 for malformed query parameters; 500 on backend read-model failure. Idempotency/Concurrency: Safe, cacheable; no idempotency key required.