Issue #3611130: Document that anonymous auto-registration is intentionally unsupported

Fons Vandammerequested to merge
issue/strava-3611130:3611130-create-a-new into 3.0.x

Replace the @todo in AthleteUserHandler::connect() with a note that anonymous visitors are deliberately not auto-registered, because the Strava API no longer exposes the athlete's email address. Linking Strava to an existing authenticated account is the supported flow.

Closes #3611130

Merge request reports