Get Active User Event

Get the user's closest-by-date active or planned event.

Back-compat surface for old mobile builds — always returns exactly one event. New clients should call GET /user_events for the full calendar.

The "no active event" case is an expected, handled outcome, not a fault: the mobile onboarding probe (auth_controller → _hasActiveUserEvent) calls this on every launch and reads a 404 as "no goal yet" — the normal state after cancelling/completing a goal, or for a brand-new user. We therefore return the 404 instead of raising HTTPException: Logfire's FastAPI instrumentation records every exception raised inside an endpoint as a span exception event (is_exception=true), so a raised 404 here floods the error views with false positives that drown real failures (#1498). Returning the response leaves the wire contract identical (same 404, same body) without emitting an exception event. Same intent as the outbound-404 policy in cheshire/telemetry.py (#1478) — keep an expected 404 out of the error views — but a different mechanism: that hook re-stamps the span level on an httpx response, this one avoids recording the exception at all. The other HTTPException(404) sites in this module signal genuinely-missing resources and stay as raises, so a real 404 is still distinguishable in telemetry (those carry an exception event; this one does not).