feat(lobby): enter the game immediately and wait for the opponent inside it

Quick auto-match no longer waits on a separate screen: Enqueue opens a real game seating the caller with an empty opponent seat (new game status 'open') and the player enters it at once. A second human searching the same variant+rule joins that open game; otherwise a background reaper seats a robot after a 90s + random 0-90s wait, pushing a new in-app opponent_joined event that fills the opponent card and re-enables resign and chat in place.

Matchmaking state is now the open games in the database (the in-memory pool, lobby.poll and lobby.cancel are gone), serialised by a per-bucket advisory lock. While a game is open the starter may move on their turn, but resign, chat and nudge are refused; the lobby and opponent card show "searching for opponent".

Schema edited in the baseline (no prod data): 'open' status, nullable game_players.account_id for the empty seat, and a games.open_deadline_at stamp; jet code regenerated.

ui/src/lib/i18n/en.ts

@@ -51,11 +51,14 @@ export const en = {
   'new.rulesRussian': '104 tiles · ё is a letter · bingo +50',
   'new.rulesErudit': '131 tiles · ё = е · no centre ×2 · bonus +15',
   'new.moveLimit': 'Move time: {n} h 00 min',
+  'new.searchHint':
+    'Finding an opponent can sometimes take a while. If you do not want to wait, close the app after starting the game and come back in a couple of minutes.',
 
   'game.bag': '{n} in the bag',
   'game.bagEmpty': 'Bag is empty',
   'game.hints': 'Hints {n}',
   'game.yourTurn': 'Your turn',
+  'game.searchingForOpponent': 'Searching for opponent…',
   'game.waiting': "Waiting for {name}",
   'game.makeMove': 'Make move',
   'game.reset': 'Reset',