Add events to existing session replay

Query-string fallback for the analytics ingest key, for clients that cannot set custom headers (navigator.sendBeacon, used to flush the final replay batch on page unload). Consulted only when the x-temps-analytics-key header is absent; identical precedence and error semantics.

Analytics ingest key (ADR-040), pa_ followed by 64 hex characters. An alternative to Host-based project resolution, for apps Temps does not deploy and which therefore have no route-table entry. When present it takes precedence and the Host header is not consulted for resolution; a key that does not resolve to an active row is a 401, never a fallback to Host. The value is public by design — it ships in client JS — and is write-only: it grants analytics ingest for one project (optionally one environment) and nothing else.