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-platform/tests/helpers.py

@@ -248,7 +248,12 @@ def make_platform(
         spec_path="/api/openapi.json",
         docs_path="/api/docs",
     )
-    scheduler = DeadlineScheduler(game_store, registry, heartbeat_ms=50)
+    scheduler = DeadlineScheduler(
+        game_store,
+        registry,
+        heartbeat_ms=50,
+        context_binder=tortoise_mixin.ensure_context,
+    )
     platform = Platform(
         registry=registry,
         game_store=game_store,