Up to 50 events of one site in one request (native SDKs)

Body: { events: [...] } — each event as for /api/collect, plus optional nonce (a per-device value the SDK regenerates every UTC day; it replaces IP + user-agent in the visitor hash) and ago (ms since the event, at most 86400000; the server subtracts it from its own clock). Each event is validated, excluded and counted on its own.