Bring back 1-minute ready-status expiry with live per-player broadcasts

A player's own browser now starts a 60s timer the moment they check
"ready" (with a visible countdown) and proactively tells the server
when it's up via a new expire_ready action - idempotent, so it only
actually clears the status if the deadline has genuinely passed.
Everyone else finds out live through a Mercure player_ready broadcast
that now carries which player and their new ready/not-ready state
(previously the broadcast payload's `ready` flag was always false due
to a stale-variable bug, though nothing consumed it yet).

checkAllPlayersReady() still does the same expiry check server-side
and broadcasts on anyone else's request in the meantime, so a stalled
frontend timer doesn't leave a stale "ready" badge showing forever.

This only affects the pre-PLAYING ready phase: checkAllPlayersReady()
still flips the session to PLAYING and stops touching ready state the
instant everyone is simultaneously ready, so the earlier fix (a reload
should never send an already-started game back to the waiting room)
is unaffected.

Also fixed the ready checkbox itself: unchecking it submitted a POST
without `toggle_ready` in the body (unchecked checkboxes aren't sent),
so un-readying silently did nothing server-side. Added the standard
hidden-fallback-input pattern to fix it.

src/Game/Controller/GameController.php

@@ -136,6 +136,11 @@ final class GameController extends AbstractController
             return $this->redirectToRoute('game', ['session' => $session->getId()]);
         }
 
+        if ($request->isMethod('POST') && $request->request->has('expire_ready')) {
+            $dashboardService->expireOwnReadyIfDue($session, $user);
+            return $this->redirectToRoute('game', ['session' => $session->getId()]);
+        }
+
         // Lazily pick up readiness changes from other players since our last request
         $dashboardService->checkAllPlayersReady($session);
 
@@ -154,17 +159,22 @@ final class GameController extends AbstractController
 
         if ($session->getStatus() === SessionStatus::READY) {
             $isReady = false;
+            $readyAt = null;
             if ($player) {
                 $settingName = SessionSettingType::tryFrom('ReadyAtForPlayer' . $player->getScreen());
                 if ($settingName) {
                     $setting = $session->getSettings()->filter(fn(SessionSetting $s) => $s->getName() === $settingName && $s->getPlayer() === $player)->first();
-                    $isReady = $setting !== null;
+                    if ($setting) {
+                        $isReady = true;
+                        $readyAt = (int)$setting->getValue();
+                    }
                 }
             }
 
             return $this->render('game/waiting.html.twig', [
                 'session' => $session,
                 'isReady' => $isReady,
+                'readyAt' => $readyAt,
                 'mercure_public_url' => $this->mercurePublicUrl,
             ]);
         }