Behavior: Validates that the specified session is still active and keeps it alive by updating its
last activity timestamp. If single-session enforcement is enabled, detects whether the session has been replaced
by a newer login. Also checks whether the user's account has expired.

Authorization: Requires a valid Bearer token ([Authorize]).

Side Effects: Updates the session's last activity timestamp. May mark the session as expired if the user account is no longer valid.

Error Scenarios: Returns 400 if the request body is null. Returns PingStatus.AccountExpired if the user or session is expired.
Returns PingStatus.SessionReplaced if single-session enforcement detected a newer session.