For non-managers /listsessions now shows player-friendly actions:
- ✅ Записаться <date> when not registered
- ✖️ Выйти <date> when already active
- ✖️ Выйти из ожидания <date> when waitlisted
Extend SessionListItemDto and the shared SQL query with IsUserActive
and IsUserWaitlisted flags so the renderer can choose the right button.
Update tests to cover all three player states.