fix: clear windowCloseAt when reopening a round

When a round is reopened (ROUND_CLOSED → ROUND_ACTIVE), the old
windowCloseAt was still in the past, causing jury submissions to fail
with "Voting window has closed" even though the round status was active.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/server/services/round-engine.ts

@@ -462,10 +462,11 @@ export async function reopenRound(
         }
       }
 
-      // Reopen this round
+      // Reopen this round — clear windowCloseAt so the voting window check
+      // doesn't reject submissions with "Voting window has closed".
       const updated = await tx.round.update({
         where: { id: roundId },
-        data: { status: 'ROUND_ACTIVE' },
+        data: { status: 'ROUND_ACTIVE', windowCloseAt: null },
       })
 
       await tx.decisionAuditLog.create({