collin/mahjong

TODO3 open

1. 1. Undo across a hand boundary

   undo() is cleared by startHand, so a 下一局 tapped by mistake — and that button sits right under someone's thumb — cannot be taken back. The deal is already reshuffled by then. Would need the snapshot from before nextHand kept, and the seed recorded, so the same wall could be rebuilt.

2. 2. Settings mid-game

   設定 is reachable from the lobby and the game-over panel, but not during a 將, so a player who wants to fix a typo'd name has to wait it out. The ? panel is already anchored per-seat and rotated to face its own edge; settings could share that treatment.

3. 3. 花槓 and other flower house rules

   Flowers score, but some tables pay 花槓 out the moment it completes rather than at settlement, and some deal 補花 differently at the start. Both are Rules flags plus a payment hook.