feature: tournament check-in, free agents, join rules and stats leaderboard

[lukepolo]

Features

Check-In — optional per tournament, off by default. Auto-scheduled window (opens/closes N minutes before start), three modes reusing the existing e_check_in_settings enum: Captains, Players, Admin. In Players mode a team is checked in once min_players_per_lineup players confirm, so substitutes aren't required. Schedule locks once the window opens.

CheckInReview — new tournament status. If every team checks in, the tournament closes registration as before. If any team misses, it is held instead of seeding. Organizers can re-admit a team, extend check-in, or continue without them. Auto-continues at start so a held tournament can never stall. No-shows are never deleted — they keep their roster and are simply excluded from seeding.

Free Agents — players register alone and are drafted into balanced teams. Selection is by sign-up time only; ELO decides which team, never who gets a slot.

Join rules — per-tournament minimum role, ELO range, invite-only + passcode, preferred regions. Gates the player being added, not just whoever clicks.

Stats leaderboard — tournament-scoped, with ADR and HLTV rating that v_tournament_player_stats doesn't carry.

Notes

• assign_seeds_to_teams and tournament_has_min_teams gate on the window having opened, not just on check_in_required — behaviour is unchanged for any tournament that doesn't use check-in.
• Check-in permissions are enforced in the action layer: the API's pooled connection carries no hasura.user, and SQL guards treat a role-less session as an internal write.
• registration_passcode is exposed via a row-level computed field, not a column permission (Hasura column permissions are per-role, not per-row).
• QA seed script: node scripts/seed-tournament-qa.mjs stands up seven tournaments covering every state.