Persist matches finished by deadline timeouts

The deadline consumer runs in a long-lived task outside any request, so
a timeout that ended the match raised 'No TortoiseContext is currently
active' in save_match_result before the state was saved: the game stayed
stuck on the last turn and the entry retried forever. It only surfaced
on the match-deciding turn; ordinary timeouts and human plays were fine.

Bind the Tortoise context before persisting a finished match (optional
context_binder wired to TortoiseMixin.ensure_context), and back off to
the heartbeat when a due entry fails instead of hot-looping on it.

server/packages/tavolo-app/src/tavolo/app.py

@@ -163,6 +163,9 @@ scheduler = DeadlineScheduler(
     game_store,
     registry,
     heartbeat_ms=settings.deadline_heartbeat_ms,
+    # The consumer task has no request context; bind the database context
+    # before it persists a match that a timeout finished.
+    context_binder=tortoise_mixin.ensure_context,
 )
 platform = Platform(
     registry=registry,