Persist "closing" as its own committed status

_close_and_draw set round_.status = "closing" but then immediately
overwrote it in memory with "closed" (no participants) or "drawing"
(with participants) before the first session.commit() — so "closing"
was never actually written to the database, only ever visible in the
ORM object's transient in-memory state. GET /rounds/current (and the
frontend's "in chiusura" label) could never observe it.

Committing right after setting "closing"/closed_at, before querying
participants, makes it a real, briefly-observable state like the
others in the round lifecycle.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/rounds/scheduler.py

@@ -77,6 +77,10 @@ class RoundScheduler:
             round_ = await session.get(Round, round_id)
             round_.status = "closing"
             round_.closed_at = datetime.now(timezone.utc)
+            # Committed on its own so "closing" is actually observable (e.g. by
+            # /rounds/current) instead of being overwritten in memory by "closed"
+            # or "drawing" below before ever reaching the database.
+            await session.commit()
 
             participants = (
                 await session.scalars(