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/e2e/quickmatch.spec.ts

@@ -0,0 +1,31 @@
+import { expect, test } from './fixtures';
+
+// The quick-match flow drops the player straight into a game that is still waiting for an
+// opponent (status 'open'): the opponent card shows "searching for opponent" and resign is
+// disabled until the mock attaches a robot shortly after, which restores the game UI. Driven
+// entirely by the mock transport (no backend).
+
+test('quick game: enter immediately, wait for an opponent, then it joins', async ({ page }) => {
+  await page.goto('/');
+  await page.getByRole('button', { name: /guest/i }).click();
+  await page.getByRole('button', { name: /New/ }).click(); // lobby tab bar -> auto-match
+
+  // Pick a variant and start; the player lands in the game at once (no "searching" screen).
+  await page.locator('.variant').first().click();
+  await page.getByRole('button', { name: /Start game/i }).click();
+  await expect(page.locator('[data-cell]').first()).toBeVisible();
+
+  // Still waiting for an opponent: the opponent card shows the placeholder, and resign (in the
+  // history panel) is disabled.
+  await expect(page.getByText(/Searching for opponent/)).toBeVisible();
+  await page.locator('.scoreboard').click(); // open the history panel
+  await expect(page.getByRole('button', { name: 'Drop game' })).toBeDisabled();
+
+  // Attach the opponent deterministically (the mock otherwise joins on a timer).
+  await page.evaluate(() => (window as unknown as { __mock: { joinOpponent(): void } }).__mock.joinOpponent());
+
+  // The opponent card shows its name, the placeholder is gone, and resign is enabled again.
+  await expect(page.getByText('Robo')).toBeVisible();
+  await expect(page.getByText(/Searching for opponent/)).toHaveCount(0);
+  await expect(page.getByRole('button', { name: 'Drop game' })).toBeEnabled();
+});