UI: add games/players stats in lobby

Need to add games stats to lobby:
* [ ] total tables;
* [ ] visible tables (with applied filters);

Extra info on players (if possible):
* [x] total players;
* [ ] busy players in games/drafts (don't count same player twice);
* [ ] free players.

Start at the lobby UI entry point and trace the existing total-players display. Determine where table visibility and player participation data are available, then verify the lobby shows total tables, filtered visible tables, total players, busy players counted once, and free players.

Written by the indexing model from the issue text.