DEFAULT_AUTOCAPTURE_EVENT_NAME

The event name an autocaptured tap is reported under when the caller doesn't choose one.

Lives here, next to ScopeStack, because it has the same reason to be shared: a hybrid app runs more than one capture pipeline (Compose, and — per #62/#63 — the native iOS and Android View surfaces), and every one of them reports the same kind of event. If each pipeline carried its own default they could drift apart silently, and the same user action would land in analytics under two different names depending on which framework happened to draw the button. A pipeline that cannot see this constant cannot stay in sync with it, so this module — the one every pipeline already depends on to read ambient context at capture time — is the narrowest place that all of them reach.