fix(analytics): the Track API payload field is 'name', not 'event'

Second half of the envelope fix: ITrackPayload is {name, properties, profileId} — sending
'event' is rejected with 400 "payload/name Invalid input: expected string", which the
module swallows by design. Verified against packages/validation/src/track.validation.ts
and the SDK's track(name, properties) signature.

backend/app/services/analytics.py

@@ -39,7 +39,9 @@ async def track(event: str, properties: dict[str, Any] | None = None, profile_id
         return
     # OpenPanel's Track API takes {type, payload:{…}} (same envelope the browser SDK
     # sends) — a flat body is rejected with 400, which this module swallows by design.
-    inner: dict[str, Any] = {"event": event, "properties": properties or {}}
+    # The payload field is "name" (ITrackPayload in packages/validation) — "event" is
+    # rejected with a 400 that this module swallows.
+    inner: dict[str, Any] = {"name": event, "properties": properties or {}}
     if profile_id:
         inner["profileId"] = profile_id
     body = {"type": "track", "payload": inner}