Publish an SSE update from the bet/withdrawal rollback paths (B-49)

_release_failed_bet and _release_failed_withdrawal restored the balance, freed
the reserved UTXOs and (for a bet) removed the participant without calling
broadcaster.publish(), so every dashboard kept showing the phantom bet and the
reduced balance until its next poll — while the success path and the
reconciler's own abandon path both published.

The two regression tests pre-open the round before subscribing: place_bet opens
one itself, and that publish() would otherwise satisfy the assertion whether or
not the rollback published anything.

app/withdrawals/service.py

@@ -173,3 +173,4 @@ async def _release_failed_withdrawal(
         user_id=user_id,
     )
     await session.commit()
+    broadcaster.publish()  # the reserved UTXOs are spendable again — refetch the balance (B-49)