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/game/Game.svelte

@@ -79,7 +79,7 @@
   let recentFlash = $state(false);
   function refreshRecent() {
     const v = view;
-    if (!v || v.game.status !== 'active') {
+    if (!v || v.game.status === 'finished') {
       recent = new Set();
       recentFlash = false;
       return;
@@ -98,8 +98,12 @@
   });
   const slots = $derived(rackView(placement));
   const rackSlots = $derived(slots.map((s) => ({ ...s, id: rackIds[s.index] ?? s.index })));
-  const isMyTurn = $derived(!!view && view.game.status === 'active' && view.game.toMove === view.seat);
-  const gameOver = $derived(!!view && view.game.status !== 'active');
+  // 'open' is an auto-match game still waiting for an opponent: the starter may move on their
+  // turn just like an active game, so "playable" covers both; only 'finished' is over.
+  const waitingForOpponent = $derived(!!view && view.game.status === 'open');
+  const playable = $derived(!!view && (view.game.status === 'active' || view.game.status === 'open'));
+  const isMyTurn = $derived(!!view && playable && view.game.toMove === view.seat);
+  const gameOver = $derived(!!view && view.game.status === 'finished');
   const bagEmpty = $derived((view?.bagLen ?? 0) === 0);
   // The seat whose move the history grid awaits with a "thinking…" placeholder: the player to
   // move while the game is active, but never the viewer themselves (their own pending cell
@@ -215,6 +219,13 @@
       if (view && e.moveCount > view.game.moveCount) void load();
     } else if (e.kind === 'game_over' && e.gameId === id) {
       applyDelta(applyGameOver(cacheSnapshot(), e.game));
+    } else if (e.kind === 'opponent_joined' && e.gameId === id && e.state) {
+      // The opponent took the empty seat: adopt the new participants and status in place,
+      // leaving the board, rack and any pending placement untouched (no refetch, no flicker).
+      if (view) {
+        view = { ...view, game: { ...view.game, seats: e.state.game.seats, status: e.state.game.status, players: e.state.game.players } };
+        setCachedGame(id, view, moves);
+      }
     } else if (e.kind === 'notify' && (e.sub === 'friend_added' || e.sub === 'friend_declined')) {
       // A request the player sent was answered: re-derive the in-game "add friend" state.
       void loadFriends();
@@ -748,10 +759,21 @@
     }
   }
 
-  // canAddFriend reports whether a seat shows the 🤝: a non-guest viewing an opponent who is
-  // not yet a friend (an already-requested opponent still shows it, but disabled).
+  // seatName renders a seat's name: "you" for the viewer, the localized "searching for
+  // opponent" placeholder for an open game's still-empty seat (no account), otherwise the
+  // display name.
+  function seatName(s: { accountId: string; displayName: string } | undefined): string {
+    if (!s) return '';
+    if (s.accountId === app.session?.userId) return t('common.you');
+    if (!s.accountId) return t('game.searchingForOpponent');
+    return s.displayName;
+  }
+
+  // canAddFriend reports whether a seat shows the 🤝: a non-guest viewing a seated opponent
+  // (not the still-empty seat of an open game) who is not yet a friend (an already-requested
+  // opponent still shows it, but disabled).
   function canAddFriend(accountId: string): boolean {
-    return !app.profile?.isGuest && accountId !== app.session?.userId && !friends.has(accountId);
+    return !!accountId && !app.profile?.isGuest && accountId !== app.session?.userId && !friends.has(accountId);
   }
 </script>
 
@@ -763,7 +785,7 @@
       {#if (app.chatUnread[id] ?? 0) > 0}<span class="cbadge sbadge">{app.chatUnread[id]}</span>{/if}
       {#each view.game.seats as s (s.seat)}
         <div class="seat" class:turn={view.game.toMove === s.seat && !gameOver} class:win={s.isWinner}>
-          <div class="nm">{s.accountId === app.session?.userId ? t('common.you') : s.displayName}</div>
+          <div class="nm">{seatName(s)}</div>
           <div class="sc">{addConfirm[s.seat] ? t('game.addFriendShort') : s.score}</div>
           {#if historyOpen && canAddFriend(s.accountId)}
             <span class="addfriend">
@@ -788,7 +810,7 @@
             {#if gameOver}
               <button class="hicon" onclick={exportGcg} aria-label={t('game.exportGcg')}>📤</button>
             {:else}
-              <button class="hicon" onclick={() => (resignOpen = true)} aria-label={t('game.dropGame')}>🏁</button>
+              <button class="hicon" onclick={() => (resignOpen = true)} disabled={waitingForOpponent} aria-label={t('game.dropGame')}>🏁</button>
             {/if}
             {#if !view.game.multipleWordsPerTurn}<span class="oneword-label">{t('game.oneWordRule')}</span>{/if}
             <button class="hicon" onclick={() => navigate(`/game/${id}/chat`)} aria-label={t('game.chat')}>
@@ -855,7 +877,7 @@
       {#if gameOver}
         <strong class="over">{t('game.over')} — {resultText()}</strong>
       {:else if placement.pending.length === 0}
-        <span class="turn-ind">{isMyTurn ? t('game.yourTurn') : view.game.seats[view.game.toMove]?.displayName ?? ''}</span>
+        <span class="turn-ind">{isMyTurn ? t('game.yourTurn') : seatName(view.game.seats[view.game.toMove])}</span>
       {/if}
       <span class="scores">
         {#if preview}{preview.legal ? t('game.previewWords', { words: preview.words.join(', '), n: preview.score }) : t('game.previewIllegal')}{:else if !view.game.multipleWordsPerTurn}<span class="oneword" title={t('game.oneWordRule')}>1️⃣</span>{/if}