Crypto ETF Sentinel — Single-call market snapshot for US spot crypto ETFs (Bitcoin, Ethereum, Solana, XRP and more). DB totals, filings broken down by cryptocurrency + form type, regulatory-stage counts (how many issuers are trading / launch_imminent / under_review / etc.), and an ``as_of`` ISO timestamp for stale-checking. Useful as a heartbeat for monitoring agents deciding whether to drill into the catalogue.