List and query the transaction ledger

Returns the billing transaction ledger for the active tenant/subscription/project scope: charges, payments, applied credits, refunds and pending wire transfers, newest first. This single endpoint backs both the plain Transactions page load (billing.transaction.list) and every search/filter/sort/pagination interaction (billing.transaction.search_filter_sort): q matches the description, the ledger reference and the linked invoice number; type and status mirror the UI counter filters (All / Payments / Charges / Pending approval); sort accepts createdAt and amount. Amounts are signed integers in ten-thousandths of the currency unit — charges positive (increase the outstanding balance), payments/credits/refunds negative. No resource state is mutated. Validation: scopeId must reference a scope visible to the caller (unknown → NOT_FOUND); type, status, sort, order, page, pageSize must be within their declared enums/ranges, otherwise VALIDATION_FAILED (422); the caller needs reader-or-higher (or billing) role in the scope, otherwise FORBIDDEN. Async & state: Synchronous read; no state change. New ledger rows posted while the view is open arrive as resource.updated SSE frames with kind billing.transaction. Errors: 401 missing/expired session; 403 caller lacks billing read permission in the scope; 404 unknown scope; 422 malformed filter/pagination parameters; 429 burst polling rate-limited; 500 ledger read-model unavailable. Idempotency/Concurrency: Safe, cacheable; no idempotency key required. Stable sort keys plus page/pageSize make repeated reads deterministic for an unchanged ledger.